Just a quick couple of notes

use CGI;
This is great you're already ahead of most new CGI programmers

print MAIL "To: $form{'usermail'}\n";
this right here, let's you become a spam portal. You have just allowed anyone who can find your page send email to anyone including UCE. You should decide if this user email is really necessary. If it is necessary preset a message; don't take a message from a form value, this will at least make it useless for spammers.

Use taint checking, to validate and clean your form data. Never trust form data.

Check out Ovid's excellent "Web Programming Using Perl" course.