This works for me on Windows:
send_mail($to, $from, $subject, $comments, $username, $userip, $useremail, $userurl, $daten, $timen);
sub send_mail {
use Net::SMTP;
my $relay = "domain.com";
my $smtp = Net::SMTP->new($relay)
|| die "Can't open mail connection: $!";
$smtp->mail($fromemail);
$smtp->to($masteremail);
$smtp->to($useremail);
$smtp->data();
$smtp->datasend("To: $masteremail\n"

;
$smtp->datasend("To: $useremail\n"

;
$smtp->datasend("From: $fromemail\n"

;
$smtp->datasend("Subject: Thank you for visiting domain.com\n"

;
$smtp->datasend("\n"

;
$smtp->datasend("\n"

;
$smtp->datasend("\n"

;
$smtp->datasend("A copy of your comments can be found below\n"

;
$smtp->datasend("======================================\n"

;
$smtp->datasend(" NAME: $username($userip) at $daten($timen)\n"

;
$smtp->datasend(" EMAIL: $useremail\n"

;
$smtp->datasend(" HOME PAGE: $userurl\n"

;
$smtp->datasend(" \n"

;
$smtp->datasend(" $comments\n"

;
$smtp->datasend("======================================\n"

;
$smtp->dataend();
}
&guestbook_succ("Thank you for signing our GuestBook!<br>Your message has been successfully posted!!"

;
} Newposter
"Good judgment comes from experience. Experience comes from bad judgment."