I don't know if you can do anything with conventional modules per se... working primarily on Windows, I don't know fork either... but I had a similar problem and in the hope of it helping you get an idea, I'll pass it on...

Write everything you need to send the mail to offline storage... For example, to a file(s), or to a database. Then, have a script running in tbe background that periodically wakes up, checks for new messages, sends the mail off, and goes back to sleep again...

This way, your users need to wait until their message is recorded in permanent storage, and then they can be away to other places...

When I did this, I gained other advantages, such as better auditing, failsafe response to the mail server being down for maintenance.. Obviously this works only if some delay between the user clicking "send mail", and actually sending the mail to the SMTP server is tolerable... YMMV
HTH