Write your own log where ever, in what ever format you want... Just add some extra Perl code to do it.

My most important advice to you is that if the input for $to, $from or $subject comes from a users input (i.e. a HTML form of a browser) make sure you check it's valid!!! Epecially check for ; : , or \r and \n. Otherwise you'll find that hackers will end up using your script to send out bulk email and you'll get all sorts of problems from you web host.
For example, they'll fill the $to field with multiple email addresses using ; , or :. Even if you check for those, and think your body text is fixed, you'll use \r and \n to add their own headers that'll disregard yours and send out what ever emails they want to whoever they want!
Take heed of that otherwise you'll end up regretting it!

Lyle