PHP mail() waits for e-mail to be sent

I'm using mail() to send email from my web app out through my ISP's mail servers. Howerver, mail() sits around and waits for the mail to be sent. Is their an asynchronous solution that my mail server ISP will be happy with? I want the mail to queue and then send without holding my script, but I don't necessarily want to implement an entire e-mail server on system. And if I do, I have XMAIL set up, but I don't understand how to get that to relay my e-mail out to ISP. I'm out of my depth!

Solution: PHP mail() waits for e-mail to be sent

To configure xmail to send the mail via your external mailserver see http://www.xmailserver.org/Readme.html#smtpgw_tab and to setup the authentication at ythat server see http://www.xmailserver.org/Readme.html#smtp_client_authentication