grep -vf exclude.list mail.list > new.list
[download]

#!/usr/bin/perl -w
#
# only-in
# find lines which are in the first file, but not in the second.
#
use strict;

die "Usage: $0 INPUT EXCLUDE\n" unless($#ARGV == 1);

my $input_file = shift;
my $exclude_file = shift;

open (INPUT, $input_file ) ||
        die("Can't open input file '$input_file': $!\n");
my @input = (<INPUT>);
close(INPUT);

open (EXCLUDE, $exclude_file ) ||
        die("Can't open exclude file '$exclude_file': $!\n");
my @exclude = (<EXCLUDE>);
close(EXCLUDE);

my @good;

for my $data (@input) {

        push (@good, $data) unless(grep /^$data$/i, @exclude);

}

print join("", @good);
[download]