If you have access to SENDMAIL, you can add something like the following:
my $user_email = 'user@email.com';
my $dist_email = 'youremail@something.com';
my $mailprog = '/usr/sbin/sendmail';
print "Content-type: text/html\n\n";
open MAIL, "| $mailprog -t -i" or die "Couldn't open Mail Program: $!";
print MAIL "To: $user_email\n";
print MAIL "From: $dist_email\n";
print MAIL "Subject: Thank you for joining....\n\n";
print MAIL "Here's your password.......";
close MAIL or die "Couldn't close Mail Program: $!";
There's always a better way...