/usr/share/perl5/auto/Mail/ListDetector/autosplit.ix is in libmail-listdetector-perl 1.03+dfsg-1.
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/Mail/ListDetector.pm
# (file acts as timestamp)
1;
|