#!/usr/bin/perl -w
use strict;

my $in_file  = 'email.log';
my $out_file = 'new_email.log'; # Note that this is written to a *different* file
                                # so we can go back if we screw up
                                # If that's not good, backup the email log.

open IN,  "< $in_file"  or die "Can't open $in_file for reading: $!";
open OUT, "> $out_file" or die "Can't open $out_file for writing: $!";

my %address;

while (<IN>) {
    print OUT, $_ if ! $address{ $_ }++;
}

close OUT or die "Can't close $out_file: $!"
close IN  or die "Can't close $in_file: $!";