Your question reads like an if statement already; so the program logic is there. What you need to do now is put together a fairly elementary control structure and consider the advice that is posted here:

How do I send an email with Perl (including an attachment)?

These kind of simple CGI scripts are so common that you could find 10 or 20 good examples if you searched groups.google.com for "perl cgi mail".

You could also look in the Snippets section here on Perlmonks, and look thru Grinders snippet index at snippet index. Then look for things under mail....like "Generic Mail Form Processor" for a start.

use Mail::Sendmail;
my %mail = (
  Subject => "test email subject",
  From => "mailchecker@localhost.localdomain",
  To => "myself@domain.com",
  body => "This message is a test.  Whee!"
);

sendmail %mail;
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