/usr/lib/x86_64-linux-gnu/perl5/5.26/auto/Sendmail/Milter/autosplit.ix is in libsendmail-milter-perl 0.18-8build3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # Index created by AutoSplit for blib/lib/Sendmail/Milter.pm
# (file acts as timestamp)
1;
|