If you want to use pschoonveld's example, you might also want to know about the -odq option to sendmail; it forces sendmail to queue the mail for sending later.

This can be helpful in situations where you are pumping out a lot of mail to different users and waiting on sendmail will slow your script down. Also bad addresses can sometimes kill your script or give you unexpected outout from sendmail in your HTML. This method will keep your output clean even if the user's email address is malformed (which you really should try to do some rudimentary checking on beforehand anyway)