It appears then that your php mail function is working, but the alert is just not being sent. Try following a couple of the steps in this thread
http://www.osticket.com/forums/showthread.php?t=1354(http://www.osticket.com/forums/showthread.php?t=1354)
pop3 only comes into play when fetching emails, not when sending them. All emails are sent using the php mail function.