This file is indexed.

/usr/bin/expn is in sendmail-base 8.15.2-3.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
#!/usr/bin/perl
'di ';
'ds 00 \\"';
'ig 00 ';
#
#       THIS PROGRAM IS ITS OWN MANUAL PAGE.  INSTALL IN man & bin.
#

use 5.001;
use IO::Socket;
use Fcntl;

# system requirements:
# 	must have 'nslookup' and 'hostname' programs.

# $OrigHeader: /home/muir/bin/RCS/expn,v 3.11 1997/09/10 08:14:02 muir Exp muir $

# TODO:
#	less magic should apply to command-line addresses
#	less magic should apply to local addresses
#	add magic to deal with cross-domain cnames
#	disconnect & reconnect after 25 commands to the same sendmail 8.8.* host

# Checklist: (hard addresses)
#	250 Kimmo Suominen <"|/usr/local/mh/lib/slocal -user kim"@grendel.tac.nyc.ny.us>
#	harry@hofmann.cs.Berkeley.EDU -> harry@tenet (.berkeley.edu)  [dead]
#	bks@cs.berkeley.edu -> shiva.CS (.berkeley.edu)		      [dead]
#	dan@tc.cornell.edu -> brown@tiberius (.tc.cornell.edu)

#############################################################################
#
#  Copyright (c) 1993 David Muir Sharnoff
#  All rights reserved.
#
#  Redistribution and use in source and binary forms, with or without
#  modification, are permitted provided that the following conditions
#  are met:
#  1. Redistributions of source code must retain the above copyright
#     notice, this list of conditions and the following disclaimer.
#  2. Redistributions in binary form must reproduce the above copyright
#     notice, this list of conditions and the following disclaimer in the
#     documentation and/or other materials provided with the distribution.
#  3. All advertising materials mentioning features or use of this software
#     must display the following acknowledgement:
#       This product includes software developed by the David Muir Sharnoff.
#  4. The name of David Sharnoff may not be used to endorse or promote products
#     derived from this software without specific prior written permission.
#
#  THIS SOFTWARE IS PROVIDED BY THE DAVID MUIR SHARNOFF ``AS IS'' AND
#  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
#  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
#  ARE DISCLAIMED.  IN NO EVENT SHALL DAVID MUIR SHARNOFF BE LIABLE
#  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
#  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
#  OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
#  HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
#  LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
#  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
#  SUCH DAMAGE.
#
# This copyright notice derrived from material copyrighted by the Regents
# of the University of California.
#
# Contributions accepted.
#
#############################################################################

# overall structure:
#	in an effort to not trace each address individually, but rather
#	ask each server in turn a whole bunch of questions, addresses to
#	be expanded are queued up.
#
#	This means that all accounting w.r.t. an address must be stored in
#	various arrays.  Generally these arrays are indexed by the
#	string "$addr *** $server" where $addr is the address to be
#	expanded "foo" or maybe "foo@bar" and $server is the hostname
#	of the SMTP server to contact.
#

# important global variables:
#
# @hosts : list of servers still to be contacted
# $server : name of the current we are currently looking at
# @users = $users{@hosts[0]} : addresses to expand at this server
# $u = $users[0] : the current address being expanded
# $names{"$users[0] *** $server"} : the 'name' associated with the address
# $mxbacktrace{"$users[0] *** $server"} : record of mx expansion
# $mx_secondary{$server} : other mx relays at the same priority
# $domainify_fallback{"$users[0] *** $server"} : alternative names to try 
#	instead of $server if $server doesn't work
# $temporary_redirect{"$users[0] *** $server"} : when trying alternates,
#	temporarily channel all tries along current path
# $giveup{$server} : do not bother expanding addresses at $server
# $verbose : -v
# $watch : -w
# $vw : -v or -w
# $debug : -d
# $valid : -a
# $levels : -1
# $S : the socket connection to $server

$have_nslookup = 1;	# we have the nslookup program
$port = 'smtp';
$av0 = $0;
$ENV{'PATH'} .= ":/usr/etc" unless $ENV{'PATH'} =~ m,/usr/etc,;
$ENV{'PATH'} .= ":/usr/ucb" unless $ENV{'PATH'} =~ m,/usr/ucb,;
select(STDERR);

$0 = "$av0 - running hostname";
chop($name = `hostname || uname -n`);

$0 = "$av0 - lookup host FQDN and IP addr";
($hostname,$aliases,$type,$len,$thisaddr) = gethostbyname($name);

$0 = "$av0 - parsing args";
$usage = "Usage: $av0 [-1avwd] user[\@host] [user2[host2] ...]";
for $a (@ARGV) {
	die $usage if $a eq "-";
	while ($a =~ s/^(-.*)([1avwd])/$1/) {
		eval '$'."flag_$2 += 1";
	}
	next if $a eq "-";
	die $usage if $a =~ /^-/;
	&expn(&parse($a,$hostname,undef,1));
}
$verbose = $flag_v;
$watch = $flag_w;
$vw = $flag_v + $flag_w;
$debug = $flag_d;
$valid = $flag_a;
$levels = $flag_1;

die $usage unless @hosts;
if ($valid) {
	if ($valid == 1) {
		$validRequirement = 0.8;
	} elsif ($valid == 2) {
		$validRequirement = 1.0;
	} elsif ($valid == 3) {
		$validRequirement = 0.9;
	} else {
		$validRequirement = (1 - (1/($valid-3)));
		print "validRequirement = $validRequirement\n" if $debug;
	}
}

HOST:
while (@hosts) {
	$server = shift(@hosts);
	@users = split(' ',$users{$server});
	delete $users{$server};

	# is this server already known to be bad?
	$0 = "$av0 - looking up $server";
	if ($giveup{$server}) {
		&giveup('mx domainify',$giveup{$server});
		next;
	}

	# do we already have an mx record for this host?
	next HOST if &mxredirect($server,*users);

	# look it up, or try for an mx.
	$0 = "$av0 - gethostbyname($server)";

	($name,$aliases,$type,$len,$thataddr) = gethostbyname($server);
	# if we can't get an A record, try for an MX record.
	unless($thataddr) {
		&mxlookup(1,$server,"$server: could not resolve name",*users);
		next HOST;
	}
				
	# get a connection, or look for an mx
	$0 = "$av0 - socket to $server";

	$S = new IO::Socket::INET (
		'PeerAddr' => $server,
		'PeerPort' => $port,
		'Proto' => 'tcp');

	if (! $S || ($debug == 10 && $server =~ /relay\d.UU.NET$/i)) {
		$0 = "$av0 - $server: could not connect: $!\n";
		$emsg = $!;
		unless (&mxlookup(0,$server,"$server: could not connect: $!",*users)) {
			&giveup('mx',"$server: Could not connect: $emsg");
		}
		next HOST;
	}
	$S->autoflush(1);

	# read the greeting
	$0 = "$av0 - talking to $server";
	&alarm("greeting with $server",'');
	while(<$S>) {
		alarm(0);
		print if $watch;
		if (/^(\d+)([- ])/) {
			if ($1 != 220) {
				$0 = "$av0 - bad numeric response from $server";
				&alarm("giving up after bad response from $server",'');
				&read_response($2,$watch);
				alarm(0);
				print STDERR "$server: NOT 220 greeting: $_"
					if ($debug || $vw);
				if (&mxlookup(0,$server,"$server: did not respond with a 220 greeting",*users)) {
					close($S);
					next HOST;
				}
			}
			last if ($2 eq " ");
		} else {
			$0 = "$av0 - bad response from $server";
			print STDERR "$server: NOT 220 greeting: $_"
				if ($debug || $vw);
			unless (&mxlookup(0,$server,"$server: did not respond with SMTP codes",*users)) {
				&giveup('',"$server: did not talk SMTP");
			}
			close($S);
			next HOST;
		}
		&alarm("greeting with $server",'');
	}
	alarm(0);
	
	# if this causes problems, remove it
	$0 = "$av0 - sending helo to $server";
	&alarm("sending helo to $server","");
	&ps("helo $hostname");
	while(<$S>) {
		print if $watch;
		last if /^\d+ /;
	}
	alarm(0);

	# try the users, one by one
	USER:
	while(@users) {
		$u = shift(@users);
		$0 = "$av0 - expanding $u [\@$server]";

		# do we already have a name for this user?
		$oldname = $names{"$u *** $server"};

		print &compact($u,$server)." ->\n" if ($verbose && ! $valid);
		if ($valid) {
			#
			# when running with -a, we delay taking any action 
			# on the results of our query until we have looked
			# at the complete output.  @toFinal stores expansions
			# that will be final if we take them.  @toExpn stores
			# expnansions that are not final.  @isValid keeps
			# track of our ability to send mail to each of the
			# expansions.
			#
			@isValid = ();
			@toFinal = ();
			@toExpn = ();
		}

#		($ecode,@expansion) = &expn_vrfy($u,$server);
		(@foo) = &expn_vrfy($u,$server);
		($ecode,@expansion) = @foo;
		if ($ecode) {
			&giveup('',$ecode,$u);
			last USER;
		}

		for $s (@expansion) {
			$s =~ s/[\n\r]//g;
			$0 = "$av0 - parsing $server: $s";

			$skipwatch = $watch;

			if ($s =~ /^[25]51([- ]).*<(.+)>/) {
				print "$s" if $watch;
				print "(pretending 250$1<$2>)" if ($debug && $watch);
				print "\n" if $watch;
				$s = "250$1<$2>";
				$skipwatch = 0;
			}

			if ($s =~ /^250([- ])(.+)/) {
				print "$s\n" if $skipwatch;
				($done,$addr) = ($1,$2);
				($newhost, $newaddr, $newname) =  &parse($addr,$server,$oldname, $#expansion == 0);
				print "($newhost, $newaddr, $newname) = &parse($addr, $server, $oldname)\n" if $debug;
				if (! $newhost) {
					# no expansion is possible w/o a new server to call
					if ($valid) {
						push(@isValid, &validAddr($newaddr));
						push(@toFinal,$newaddr,$server,$newname);
					} else {
						&verbose(&final($newaddr,$server,$newname));
					}
				} else {
					$newmxhost = &mx($newhost,$newaddr);
					print "$newmxhost = &mx($newhost)\n" 
						if ($debug && $newhost ne $newmxhost);
					$0 = "$av0 - parsing $newaddr [@$newmxhost]";
					print "levels = $levels, level{$u *** $server} = ".$level{"$u *** $server"}."\n" if ($debug > 1);
					# If the new server is the current one, 
					# it would have expanded things for us
					# if it could have.  Mx records must be
					# followed to compare server names.
					# We are also done if the recursion
					# count has been exceeded.
					if (&trhost($newmxhost) eq &trhost($server) || ($levels && $level{"$u *** $server"} >= $levels)) {
						if ($valid) {
							push(@isValid, &validAddr($newaddr));
							push(@toFinal,$newaddr,$newmxhost,$newname);
						} else {
							&verbose(&final($newaddr,$newmxhost,$newname));
						}
					} else {
						# more work to do...
						if ($valid) {
							push(@isValid, &validAddr($newaddr));
							push(@toExpn,$newmxhost,$newaddr,$newname,$level{"$u *** $server"});
						} else {
							&verbose(&expn($newmxhost,$newaddr,$newname,$level{"$u *** $server"}));
						}
					}
				}
				last if ($done eq " ");
				next;
			}
			# 550 is a known code...  Should the be
			# included in -a output?  Might be a bug
			# here.  Does it matter?  Can assume that
			# there won't be UNKNOWN USER responses 
			# mixed with valid users?
			if ($s =~ /^(550)([- ])/) {
				if ($valid) {
					print STDERR "\@$server:$u ($oldname) USER UNKNOWN\n";
				} else {
					&verbose(&final($u,$server,$oldname,"USER UNKNOWN"));
				}
				last if ($2 eq " ");
				next;
			} 
			# 553 is a known code...  
			if ($s =~ /^(553)([- ])/) {
				if ($valid) {
					print STDERR "\@$server:$u ($oldname) USER AMBIGUOUS\n";
				} else {
					&verbose(&final($u,$server,$oldname,"USER AMBIGUOUS"));
				}
				last if ($2 eq " ");
				next;
			} 
			# 252 is a known code...  
			if ($s =~ /^(252)([- ])/) {
				if ($valid) {
					print STDERR "\@$server:$u ($oldname) REFUSED TO VRFY\n";
				} else {
					&verbose(&final($u,$server,$oldname,"REFUSED TO VRFY"));
				}
				last if ($2 eq " ");
				next;
			} 
			&giveup('',"$server: did not grok '$s'",$u);
			last USER;
		}

		if ($valid) {
			#
			# now we decide if we are going to take these
			# expansions or roll them back.
			#
			$avgValid = &average(@isValid);
			print "avgValid = $avgValid\n" if $debug;
			if ($avgValid >= $validRequirement) {
				print &compact($u,$server)." ->\n" if $verbose;
				while (@toExpn) {
					&verbose(&expn(splice(@toExpn,0,4)));
				}
				while (@toFinal) {
					&verbose(&final(splice(@toFinal,0,3)));
				}
			} else {
				print "Tossing some valid to avoid invalid ".&compact($u,$server)."\n" if ($avgValid > 0.0 && ($vw || $debug));
				print &compact($u,$server)." ->\n" if $verbose;
				&verbose(&final($u,$server,$newname));
			}
		}
	}

	&alarm("sending 'quit' to $server",'');
	$0 = "$av0 - sending 'quit' to $server";
	&ps("quit");
	while(<$S>) {
		print if $watch;
		last if /^\d+ /;
	}
	close($S);
	alarm(0);
}

$0 = "$av0 - printing final results";
print "----------\n" if $vw;
select(STDOUT);
for $f (sort @final) {
	print "$f\n";
}
unlink("/tmp/expn$$");
exit(0);


# abandon all attempts deliver to $server
# register the current addresses as the final ones
sub giveup
{
	local($redirect_okay,$reason,$user) = @_;
	local($us,@so,$nh,@remaining_users);
	local($pk,$file,$line);
	($pk, $file, $line) = caller;

	$0 = "$av0 - giving up on $server: $reason";
	#
	# add back a user if we gave up in the middle
	#
	push(@users,$user) if $user;
	#
	# don't bother with this system anymore
	#
	unless ($giveup{$server}) {
		$giveup{$server} = $reason;
		print STDERR "$reason\n";
	}
	print "Giveup at $file:$line!!! redirect okay = $redirect_okay; $reason\n" if $debug;
	#
	# Wait!
	# Before giving up, see if there is a chance that
	# there is another host to redirect to!
	# (Kids, don't do this at home!  Hacking is a dangerous
	# crime and you could end up behind bars.)
	#
	for $u (@users) {
		if ($redirect_okay =~ /\bmx\b/) {
			next if &try_fallback('mx',$u,*server,
				*mx_secondary,
				*already_mx_fellback);
		}
		if ($redirect_okay =~ /\bdomainify\b/) {
			next if &try_fallback('domainify',$u,*server,
				*domainify_fallback,
				*already_domainify_fellback);
		}
		push(@remaining_users,$u);
	}
	@users = @remaining_users;
	for $u (@users) {
		print &compact($u,$server)." ->\n" if ($verbose && $valid && $u);
		&verbose(&final($u,$server,$names{"$u *** $server"},$reason));
	}
}
#
# This routine is used only within &giveup.  It checks to
# see if we really have to giveup or if there is a second
# chance because we did something before that can be 
# backtracked.
#
# %fallback{"$user *** $host"} tracks what is able to fallback
# %fellback{"$user *** $host"} tracks what has fallen back
#
# If there is a valid backtrack, then queue up the new possibility
#
sub try_fallback
{
	local($method,$user,*host,*fall_table,*fellback) = @_;
	local($us,$fallhost,$oldhost,$ft,$i);

	if ($debug > 8) {
		print "Fallback table $method:\n";
		for $i (sort keys %fall_table) {
			print "\t'$i'\t\t'$fall_table{$i}'\n";
		}
		print "Fellback table $method:\n";
		for $i (sort keys %fellback) {
			print "\t'$i'\t\t'$fellback{$i}'\n";
		}
		print "U: $user H: $host\n";
	}
	
	$us = "$user *** $host";
	if (defined $fellback{$us}) {
		#
		# Undo a previous fallback so that we can try again
		# Nested fallbacks are avoided because they could
		# lead to infinite loops
		#
		$fallhost = $fellback{$us};
		print "Already $method fell back from $us -> \n" if $debug;
		$us = "$user *** $fallhost";
		$oldhost = $fallhost;
	} elsif (($method eq 'mx') && (defined $mxbacktrace{$us}) && (defined $mx_secondary{$mxbacktrace{$us}})) {
		print "Fallback an MX expansion $us -> \n" if $debug;
		$oldhost = $mxbacktrace{$us};
	} else {
		print "Oldhost($host, $us) = " if $debug;
		$oldhost = $host;
	}
	print "$oldhost\n" if $debug;
	if (((defined $fall_table{$us}) && ($ft = $us)) || ((defined $fall_table{$oldhost}) && ($ft = $oldhost))) {
		print "$method Fallback = ".$fall_table{$ft}."\n" if $debug;
		local(@so,$newhost);
		@so = split(' ',$fall_table{$ft});
		$newhost = shift(@so);
		print "Falling back ($method) $us -> $newhost (from $oldhost)\n" if $debug;
		if ($method eq 'mx') {
			if (! defined ($mxbacktrace{"$user *** $newhost"})) {
				if (defined $mxbacktrace{"$user *** $oldhost"}) {
					print "resetting oldhost $oldhost to the original: " if $debug;
					$oldhost = $mxbacktrace{"$user *** $oldhost"};
					print "$oldhost\n" if $debug;
				}
				$mxbacktrace{"$user *** $newhost"} = $oldhost;
				print "mxbacktrace $user *** $newhost -> $oldhost\n" if $debug;
			}
			$mx{&trhost($oldhost)} = $newhost;
		} else {
			$temporary_redirect{$us} = $newhost;
		}
		if (@so) {
			print "Can still $method  $us: @so\n" if $debug;
			$fall_table{$ft} = join(' ',@so);
		} else {
			print "No more fallbacks for $us\n" if $debug;
			delete $fall_table{$ft};
		}
		if (defined $create_host_backtrack{$us}) {
			$create_host_backtrack{"$user *** $newhost"} 
				= $create_host_backtrack{$us};
		}
		$fellback{"$user *** $newhost"} = $oldhost;
		&expn($newhost,$user,$names{$us},$level{$us});
		return 1;
	}
	delete $temporary_redirect{$us};
	$host = $oldhost;
	return 0;
}
# return 1 if you could send mail to the address as is.
sub validAddr
{
	local($addr) = @_;
	$res = &do_validAddr($addr);
	print "validAddr($addr) = $res\n" if $debug;
	$res;
}
sub do_validAddr
{
	local($addr) = @_;
	local($urx) = "[-A-Za-z_.0-9+]+";

	# \u
	return 0 if ($addr =~ /^\\/);
	# ?@h
	return 1 if ($addr =~ /.\@$urx$/);
	# @h:?
	return 1 if ($addr =~ /^\@$urx\:./);
	# h!u
	return 1 if ($addr =~ /^$urx!./);
	# u
	return 1 if ($addr =~ /^$urx$/);
	# ?
	print "validAddr($addr) = ???\n" if $debug;
	return 0;
}
# Some systems use expn and vrfy interchangeably.  Some only
# implement one or the other.  Some check expn against mailing
# lists and vrfy against users.  It doesn't appear to be
# consistent.
#
# So, what do we do?  We try everything!
#
#
# Ranking of result codes: good: 250, 251/551, 252, 550, anything else
#
# Ranking of inputs: best: user@host.domain, okay: user
#
# Return value: $error_string, @responses_from_server
sub expn_vrfy
{
	local($u,$server) = @_;
	local(@c) = ('expn', 'vrfy');
	local(@try_u) = $u;
	local(@ret,$code);

	if (($u =~ /(.+)@(.+)/) && (&trhost($2) eq &trhost($server))) {
		push(@try_u,$1);
	}

	TRY:
	for $c (@c) {
		for $try_u (@try_u) {
			&alarm("${c}'ing $try_u on $server",'',$u);
			&ps("$c $try_u");
			alarm(0);
			$s = <$S>;
			if ($s eq '') {
				return "$server: lost connection";
			}
			if ($s !~ /^(\d+)([- ])/) {
				return "$server: garbled reply to '$c $try_u'";
			}
			if ($1 == 250) {
				$code = 250;
				@ret = ("",$s);
				push(@ret,&read_response($2,$debug));
				return (@ret);
			} 
			if ($1 == 551 || $1 == 251) {
				$code = $1;
				@ret = ("",$s);
				push(@ret,&read_response($2,$debug));
				next;
			}
			if ($1 == 252 && ($code == 0 || $code == 550)) {
				$code = 252;
				@ret = ("",$s);
				push(@ret,&read_response($2,$watch));
				next;
			}
			if ($1 == 550 && $code == 0) {
				$code = 550;
				@ret = ("",$s);
				push(@ret,&read_response($2,$watch));
				next;
			}
			&read_response($2,$watch);
		}
	}
	return "$server: expn/vrfy not implemented" unless @ret;
	return @ret;
}
# sometimes the old parse routine (now parse2) didn't
# reject funky addresses. 
sub parse
{
	local($oldaddr,$server,$oldname,$one_to_one) = @_;
	local($newhost, $newaddr, $newname, $um) =  &parse2($oldaddr,$server,$oldname,$one_to_one);
	if ($newaddr =~ m,^["/],) {
		return (undef, $oldaddr, $newname) if $valid;
		return (undef, $um, $newname);
	}
	return ($newhost, $newaddr, $newname);
}

# returns ($new_smtp_server,$new_address,$new_name)
# given a response from a SMTP server ($newaddr), the 
# current host ($server), the old "name" and a flag that
# indicates if it is being called during the initial 
# command line parsing ($parsing_args)
sub parse2
{
	local($newaddr,$context_host,$old_name,$parsing_args) = @_;
	local(@names) = $old_name;
	local($urx) = "[-A-Za-z_.0-9+]+";
	local($unmangle);

	#
	# first, separate out the address part.
	#

	#
	# [NAME] <ADDR [(NAME)]>
	# [NAME] <[(NAME)] ADDR
	# ADDR [(NAME)]
	# (NAME) ADDR
	# [(NAME)] <ADDR>
	#
	if ($newaddr =~ /^\<(.*)\>$/) {
		print "<A:$1>\n" if $debug;
		($newaddr) = &trim($1);
		print "na = $newaddr\n" if $debug;
	}
	if ($newaddr =~ /^([^\<\>]*)\<([^\<\>]*)\>([^\<\>]*)$/) {
		# address has a < > pair in it.
		print "N:$1 <A:$2> N:$3\n" if $debug;
		($newaddr) = &trim($2);
		unshift(@names, &trim($3,$1));
		print "na = $newaddr\n" if $debug;
	}
	if ($newaddr =~ /^([^\(\)]*)\(([^\(\)]*)\)([^\(\)]*)$/) {
		# address has a ( ) pair in it.
		print "A:$1 (N:$2) A:$3\n" if $debug;
		unshift(@names,&trim($2));
		local($f,$l) = (&trim($1),&trim($3));
		if (($f && $l) || !($f || $l)) {
			# address looks like:
			# foo (bar) baz  or (bar)
			# not allowed!
			print STDERR "Could not parse $newaddr\n" if $vw;
			return(undef,$newaddr,&firstname(@names));
		}
		$newaddr = $f if $f;
		$newaddr = $l if $l;
		print "newaddr now = $newaddr\n" if $debug;
	}
	#
	# @foo:bar
	# j%k@l
	# a@b
	# b!a
	# a
	#
	$unmangle = $newaddr;
	if ($newaddr =~ /^\@($urx)\:(.+)$/) {
		print "(\@:)" if $debug;
		# this is a bit of a cheat, but it seems necessary
		return (&domainify($1,$context_host,$2),$2,&firstname(@names),$unmangle);
	}
	if ($newaddr =~ /^(.+)\@($urx)$/) {
		print "(\@)" if $debug;
		return (&domainify($2,$context_host,$newaddr),$newaddr,&firstname(@names),$unmangle);
	}
	if ($parsing_args) {
		if ($newaddr =~ /^($urx)\!(.+)$/) {
			return (&domainify($1,$context_host,$newaddr),$newaddr,&firstname(@names),$unmangle);
		}
		if ($newaddr =~ /^($urx)$/) {
			return ($context_host,$newaddr,&firstname(@names),$unmangle);
		}
		print STDERR "Could not parse $newaddr\n";
	}
	print "(?)" if $debug;
	return(undef,$newaddr,&firstname(@names),$unmangle);
}
# return $u (@$server) unless $u includes reference to $server
sub compact
{
	local($u, $server) = @_;
	local($se) = $server;
	local($sp);
	$se =~ s/(\W)/\\$1/g;
	$sp = " (\@$server)";
	if ($u !~ /$se/i) {
		return "$u$sp";
	}
	return $u;
}
# remove empty (spaces don't count) members from an array
sub trim
{
	local(@v) = @_;
	local($v,@r);
	for $v (@v) {
		$v =~ s/^\s+//;
		$v =~ s/\s+$//;
		push(@r,$v) if ($v =~ /\S/);
	}
	return(@r);
}
# using the host part of an address, and the server name, add the
# servers' domain to the address if it doesn't already have a 
# domain.  Since this sometimes fails, save a back reference so
# it can be unrolled.
sub domainify
{
	local($host,$domain_host,$u) = @_;
	local($domain,$newhost);

	# cut of trailing dots 
	$host =~ s/\.$//;
	$domain_host =~ s/\.$//;

	if ($domain_host !~ /\./) {
		#
		# domain host isn't, keep $host whatever it is
		#
		print "domainify($host,$domain_host) = $host\n" if $debug;
		return $host;
	}

	# 
	# There are several weird situtations that need to be 
	# accounted for.  They have to do with domain relay hosts.
	#
	# Examples: 
	#	host		server		"right answer"
	#	
	#	shiva.cs	cs.berkeley.edu	shiva.cs.berkeley.edu
	#	shiva		cs.berkeley.edu	shiva.cs.berekley.edu
	#	cumulus		reed.edu	@reed.edu:cumulus.uucp
	# 	tiberius	tc.cornell.edu	tiberius.tc.cornell.edu
	#
	# The first try must always be to cut the domain part out of 
	# the server and tack it onto the host.
	#
	# A reasonable second try is to tack the whole server part onto
	# the host and for each possible repeated element, eliminate 
	# just that part.
	#
	# These extra "guesses" get put into the %domainify_fallback
	# array.  They will be used to give addresses a second chance
	# in the &giveup routine
	#

	local(%fallback);

	local($long); 
	$long = "$host $domain_host";
	$long =~ tr/A-Z/a-z/;
	print "long = $long\n" if $debug;
	if ($long =~ s/^([^ ]+\.)([^ ]+) \2(\.[^ ]+\.[^ ]+)/$1$2$3/) {
		# matches shiva.cs cs.berkeley.edu and returns shiva.cs.berkeley.edu
		print "condensed fallback $host $domain_host -> $long\n" if $debug;
		$fallback{$long} = 9;
	}

	local($fh);
	$fh = $domain_host;
	while ($fh =~ /\./) {
		print "FALLBACK $host.$fh = 1\n" if $debug > 7;
		$fallback{"$host.$fh"} = 1;
		$fh =~ s/^[^\.]+\.//;
	}

	$fallback{"$host.$domain_host"} = 2;

	($domain = $domain_host) =~ s/^[^\.]+//;
	$fallback{"$host$domain"} = 6
		if ($domain =~ /\./);

	if ($host =~ /\./) {
		#
		# Host is already okay, but let's look for multiple
		# interpretations
		#
		print "domainify($host,$domain_host) = $host\n" if $debug;
		delete $fallback{$host};
		$domainify_fallback{"$u *** $host"} = join(' ',sort {$fallback{$b} <=> $fallback{$a};} keys %fallback) if %fallback;
		return $host;
	}

	$domain = ".$domain_host"
		if ($domain !~ /\..*\./);
	$newhost = "$host$domain";

	$create_host_backtrack{"$u *** $newhost"} = $domain_host;
	print "domainify($host,$domain_host) = $newhost\n" if $debug;
	delete $fallback{$newhost};
	$domainify_fallback{"$u *** $newhost"} = join(' ',sort {$fallback{$b} <=> $fallback{$a};} keys %fallback) if %fallback;
	if ($debug) {
		print "fallback = ";
		print $domainify_fallback{"$u *** $newhost"} 
			if defined($domainify_fallback{"$u *** $newhost"});
		print "\n";
	}
	return $newhost;
}
# return the first non-empty element of an array
sub firstname
{
	local(@names) = @_;
	local($n);
	while(@names) {
		$n = shift(@names);
		return $n if $n =~ /\S/;
	}
	return undef;
}
# queue up more addresses to expand
sub expn
{
	local($host,$addr,$name,$level) = @_;
	if ($host) {
		$host = &trhost($host);

		if (($debug > 3) || (defined $giveup{$host})) {
			unshift(@hosts,$host) unless $users{$host};
		} else {
			push(@hosts,$host) unless $users{$host};
		}
		$users{$host} .= " $addr";
		$names{"$addr *** $host"} = $name;
		$level{"$addr *** $host"} = $level + 1;
		print "expn($host,$addr,$name)\n" if $debug;
		return "\t$addr\n";
	} else {
		return &final($addr,'NONE',$name);
	}
}
# compute the numerical average value of an array
sub average
{
	local(@e) = @_;
	return 0 unless @e;
	local($e,$sum);
	for $e (@e) {
		$sum += $e;
	}
	$sum / @e;
}
# print to the server (also to stdout, if -w)
sub ps
{
	local($p) = @_;
	print ">>> $p\n" if $watch;
	print $S "$p\n";
}
# return case-adjusted name for a host (for comparison purposes)
sub trhost 
{
	# treat foo.bar as an alias for Foo.BAR
	local($host) = @_;
	local($trhost) = $host;
	$trhost =~ tr/A-Z/a-z/;
	if ($trhost{$trhost}) {
		$host = $trhost{$trhost};
	} else {
		$trhost{$trhost} = $host;
	}
	$trhost{$trhost};
}
# re-queue users if an mx record dictates a redirect
# don't allow a user to be redirected more than once
sub mxredirect
{
	local($server,*users) = @_;
	local($u,$nserver,@still_there);

	$nserver = &mx($server);

	if (&trhost($nserver) ne &trhost($server)) {
		$0 = "$av0 - mx redirect $server -> $nserver\n";
		for $u (@users) {
			if (defined $mxbacktrace{"$u *** $nserver"}) {
				push(@still_there,$u);
			} else {
				$mxbacktrace{"$u *** $nserver"} = $server;
				print "mxbacktrace{$u *** $nserver} = $server\n"
					if ($debug > 1);
				&expn($nserver,$u,$names{"$u *** $server"});
			}
		}
		@users = @still_there;
		if (! @users) {
			return $nserver;
		} else {
			return undef;
		}
	}
	return undef;
}
# follow mx records, return a hostname
# also follow temporary redirections comming from &domainify and
# &mxlookup
sub mx
{
	local($h,$u) = @_;

	for (;;) {
		if (defined $mx{&trhost($h)} && $h ne $mx{&trhost($h)}) {
			$0 = "$av0 - mx expand $h";
			$h = $mx{&trhost($h)};
			return $h;
		}
		if ($u) {
			if (defined $temporary_redirect{"$u *** $h"}) {
				$0 = "$av0 - internal redirect $h";
				print "Temporary redirect taken $u *** $h -> " if $debug;
				$h = $temporary_redirect{"$u *** $h"};
				print "$h\n" if $debug;
				next;
			}
			$htr = &trhost($h);
			if (defined $temporary_redirect{"$u *** $htr"}) {
				$0 = "$av0 - internal redirect $h";
				print "temporary redirect taken $u *** $h -> " if $debug;
				$h = $temporary_redirect{"$u *** $htr"};
				print "$h\n" if $debug;
				next;
			}
		}
		return $h;
	}
}
# look up mx records with the name server.
# re-queue expansion requests if possible
# optionally give up on this host.
sub mxlookup 
{
	local($lastchance,$server,$giveup,*users) = @_;
	local(*T);
	local(*NSLOOKUP);
	local($nh, $pref,$cpref);
	local($o0) = $0;
	local($nserver);
	local($name,$aliases,$type,$len,$thataddr);
	local(%fallback);

	return 1 if &mxredirect($server,*users);

	if ((defined $mx{$server}) || (! $have_nslookup)) {
		return 0 unless $lastchance;
		&giveup('mx domainify',$giveup);
		return 0;
	}

	$0 = "$av0 - nslookup of $server";
	sysopen(T,"/tmp/expn$$",O_RDWR|O_CREAT|O_EXCL,0600) || die "open > /tmp/expn$$: $!\n";
	print T "set querytype=MX\n";
	print T "$server\n";
	close(T);
	$cpref = 1.0E12;
	undef $nserver;
	open(NSLOOKUP,"nslookup < /tmp/expn$$ 2>&1 |") || die "open nslookup: $!";
	while(<NSLOOKUP>) {
		print if ($debug > 2);
		if (/mail exchanger = ([-A-Za-z_.0-9+]+)/) {
			$nh = $1;
			if (/preference = (\d+)/) {
				$pref = $1;
				if ($pref < $cpref) {
					$nserver = $nh;
					$cpref = $pref;
				} elsif ($pref) {
					$fallback{$pref} .= " $nh";
				}
			}
		}
		if (/Non-existent domain/) {
			#
			# These addresss are hosed.  Kaput!  Dead! 
			# However, if we created the address in the
			# first place then there is a chance of 
			# salvation.
			#
			1 while(<NSLOOKUP>);	
			close(NSLOOKUP);
			return 0 unless $lastchance;
			&giveup('domainify',"$server: Non-existent domain",undef,1);
			return 0;	
		}
				
	}
	close(NSLOOKUP);
	unlink("/tmp/expn$$");
	unless ($nserver) {
		$0 = "$o0 - finished mxlookup";
		return 0 unless $lastchance;
		&giveup('mx domainify',"$server: Could not resolve address");
		return 0;
	}

	# provide fallbacks in case $nserver doesn't work out
	if (defined $fallback{$cpref}) {
		$mx_secondary{$server} = $fallback{$cpref};
	}

	$0 = "$av0 - gethostbyname($nserver)";
	($name,$aliases,$type,$len,$thataddr) = gethostbyname($nserver);

	unless ($thataddr) {
		$0 = $o0;
		return 0 unless $lastchance;
		&giveup('mx domainify',"$nserver: could not resolve address");
		return 0;
	}
	print "MX($server) = $nserver\n" if $debug;
	print "$server -> $nserver\n" if $vw && !$debug;
	$mx{&trhost($server)} = $nserver;
	# redeploy the users
	unless (&mxredirect($server,*users)) {
		return 0 unless $lastchance;
		&giveup('mx domainify',"$nserver: only one level of mx redirect allowed");
		return 0;
	}
	$0 = "$o0 - finished mxlookup";
	return 1;
}
# if mx expansion did not help to resolve an address
# (ie: foo@bar became @baz:foo@bar, then undo the 
# expansion).
# this is only used by &final
sub mxunroll
{
	local(*host,*addr) = @_;
	local($r) = 0;
	print "looking for mxbacktrace{$addr *** $host}\n"
		if ($debug > 1);
	while (defined $mxbacktrace{"$addr *** $host"}) {
		print "Unrolling MX expnasion: \@$host:$addr -> " 
			if ($debug || $verbose);
		$host = $mxbacktrace{"$addr *** $host"};
		print "\@$host:$addr\n" 
			if ($debug || $verbose);
		$r = 1;
	}
	return 1 if $r;
	$addr = "\@$host:$addr"
		if ($host =~ /\./);
	return 0;
}
# register a completed expnasion.  Make the final address as 
# simple as possible.
sub final
{
	local($addr,$host,$name,$error) = @_;
	local($he);
	local($hb,$hr);
	local($au,$ah);

	if ($error =~ /Non-existent domain/) {
		# 
		# If we created the domain, then let's undo the
		# damage...
		#
		if (defined $create_host_backtrack{"$addr *** $host"}) {
			while (defined $create_host_backtrack{"$addr *** $host"}) {
				print "Un&domainifying($host) = " if $debug;
				$host = $create_host_backtrack{"$addr *** $host"};
				print "$host\n" if $debug;
			}
			$error = "$host: could not locate";
		} else {
			# 
			# If we only want valid addresses, toss out
			# bad host names.
			#
			if ($valid) {
				print STDERR "\@$host:$addr ($name) Non-existent domain\n";
				return "";
			}
		}
	}

	MXUNWIND: {
		$0 = "$av0 - final parsing of \@$host:$addr";
		($he = $host) =~ s/(\W)/\\$1/g;
		if ($addr !~ /@/) {
			# addr does not contain any host
			$addr = "$addr@$host";
		} elsif ($addr !~ /$he/i) {
			# if host part really something else, use the something
			# else.
			if ($addr =~ m/(.*)\@([^\@]+)$/) {
				($au,$ah) = ($1,$2);
				print "au = $au ah = $ah\n" if $debug;
				if (defined $temporary_redirect{"$addr *** $ah"}) {
					$addr = "$au\@".$temporary_redirect{"$addr *** $ah"};
					print "Rewrite! to $addr\n" if $debug;
					next MXUNWIND;
				}
			}
			# addr does not contain full host
			if ($valid) {
				if ($host =~ /^([^\.]+)(\..+)$/) {
					# host part has a . in it - foo.bar
					($hb, $hr) = ($1, $2);
					if ($addr =~ /\@([^\.\@]+)$/ && ($1 eq $hb)) {
						# addr part has not . 
						# and matches beginning of
						# host part -- tack on a 
						# domain name.
						$addr .= $hr;
					} else {
						&mxunroll(*host,*addr) 
							&& redo MXUNWIND;
					}
				} else {
					&mxunroll(*host,*addr) 
						&& redo MXUNWIND;
				}
			} else {
				$addr = "${addr}[\@$host]"
					if ($host =~ /\./);
			}
		}
	}
	$name = "$name " if $name;
	$error = " $error" if $error;
	if ($valid) {
		push(@final,"$name<$addr>");
	} else {
		push(@final,"$name<$addr>$error");
	}
	"\t$name<$addr>$error\n";
}

sub alarm
{
	local($alarm_action,$alarm_redirect,$alarm_user) = @_;
	alarm(3600);
	$SIG{ALRM} = 'handle_alarm';
}
# this involves one great big ugly hack.
# the "next HOST" unwinds the stack!
sub handle_alarm
{
	&giveup($alarm_redirect,"Timed out during $alarm_action",$alarm_user);
	next HOST;
}

# read the rest of the current smtp daemon's response (and toss it away)
sub read_response
{
	local($done,$watch) = @_;
	local(@resp);
	print $s if $watch;
	while(($done eq "-") && ($s = <$S>) && ($s =~ /^\d+([- ])/)) {
		print $s if $watch;
		$done = $1;
		push(@resp,$s);
	}
	return @resp;
}
# print args if verbose.  Return them in any case
sub verbose
{
	local(@tp) = @_;
	print "@tp" if $verbose;
}
# to pass perl -w:
@tp;
$flag_a;
$flag_d;
$flag_1;
%already_domainify_fellback;
%already_mx_fellback;
&handle_alarm;
################### BEGIN PERL/TROFF TRANSITION 
.00 ;	

'di
.nr nl 0-1
.nr % 0
.\\"'; __END__ 
.\" ############## END PERL/TROFF TRANSITION
.TH EXPN 1 "March 11, 1993"
.AT 3
.SH NAME
expn \- recursively expand mail aliases
.SH SYNOPSIS
.B expn
.RI [ -a ]
.RI [ -v ]
.RI [ -w ]
.RI [ -d ]
.RI [ -1 ]
.IR user [@ hostname ]
.RI [ user [@ hostname ]]...
.SH DESCRIPTION
.B expn
will use the SMTP
.B expn
and 
.B vrfy
commands to expand mail aliases.  
It will first look up the addresses you provide on the command line.
If those expand into addresses on other systems, it will 
connect to the other systems and expand again.  It will keep 
doing this until no further expansion is possible.
.SH OPTIONS
The default output of 
.B expn
can contain many lines which are not valid
email addresses.  With the 
.I -aa
flag, only expansions that result in legal addresses
are used.  Since many mailing lists have an illegal
address or two, the single
.IR -a ,
address, flag specifies that a few illegal addresses can
be mixed into the results.   More 
.I -a
flags vary the ratio.  Read the source to track down
the formula.  With the
.I -a
option, you should be able to construct a new mailing
list out of an existing one.
.LP
If you wish to limit the number of levels deep that 
.B expn
will recurse as it traces addresses, use the
.I -1
option.  For each 
.I -1
another level will be traversed.  So, 
.I -111
will traverse no more than three levels deep.
.LP
The normal mode of operation for
.B expn
is to do all of its work silently.
The following options make it more verbose.
It is not necessary to make it verbose to see what it is
doing because as it works, it changes its 
.BR argv [0]
variable to reflect its current activity.
To see how it is expanding things, the 
.IR -v ,
verbose, flag will cause 
.B expn 
to show each address before
and after translation as it works.
The 
.IR -w ,
watch, flag will cause
.B expn
to show you its conversations with the mail daemons.
Finally, the 
.IR -d ,
debug, flag will expose many of the inner workings so that
it is possible to eliminate bugs.
.SH ENVIRONMENT
No environment variables are used.
.SH FILES
.PD 0
.B /tmp/expn$$
.B temporary file used as input to 
.BR nslookup .
.SH SEE ALSO
.BR aliases (5), 
.BR sendmail (8),
.BR nslookup (8),
RFC 823, and RFC 1123.
.SH BUGS
Not all mail daemons will implement 
.B expn
or
.BR vrfy .
It is not possible to verify addresses that are served
by such daemons.
.LP
When attempting to connect to a system to verify an address,
.B expn
only tries one IP address.  Most mail daemons
will try harder.
.LP
It is assumed that you are running domain names and that 
the 
.BR nslookup (8) 
program is available.  If not, 
.B expn
will not be able to verify many addresses.  It will also pause
for a long time unless you change the code where it says
.I $have_nslookup = 1
to read
.I $have_nslookup = 
.IR 0 .
.LP
Lastly, 
.B expn
does not handle every valid address.  If you have an example,
please submit a bug report.
.SH CREDITS
In 1986 or so, Jon Broome wrote a program of the same name
that did about the same thing.  It has since suffered bit rot
and Jon Broome has dropped off the face of the earth!
(Jon, if you are out there, drop me a line)
.SH AVAILABILITY
The latest version of 
.B expn
is available through anonymous ftp at
.IR ftp://ftp.idiom.com/pub/muir-programs/expn .
.SH AUTHOR
.I David Muir Sharnoff\ \ \ \ <muir@idiom.com>