my $file = "emails.txt";
    open(FILE, $file) or die "cannot open $file : $!\n";
    @content = reverse (<FILE>);
    close FILE;

print "<textarea cols=\"75\" rows=\"22\">";
foreach $address (@content) {
chomp($address);
print $address;
if ($address ne $content[-1]){print ", "}
}
print "</textarea>";

##</code><code>##

..
my $counter=0;
foreach $address (@content) {
chomp($address);
print $address;
$counter++;
if ($counter < @content){print ", "}
}
..