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

my $ifile = shift || die "No filename provided\n";
open IFILE, '<', "$ifile"    || die "Couldn't open file: $!";
open OFILE, '+>', 'new-data' || die "Couldn't open outfile: $!";
chomp(my @lines = <IFILE>);
close IFILE;

my @matches = map { /^@.*mail(\d+).*\z/? $1 <= 8? $1: ( ): $_ } @lines;

map { print OFILE "$_\n" } @matches;
close OFILE;