/inet\ addr:(\d+\.\d+\.\d+\.\d+)\s+.*$/;
...
print MAIL $1;
[download]

I'd fail this in a code review. You've not assured a match on the regex, so the $1 there could be the previous $1, since the dollar vars are not updated on an unsuccessful match.

At the very minimum, put "or die" after the match.

-- Randal L. Schwartz, Perl hacker