outgoing mail function freezing problem

Hello there Thanks for all with the help yesterday My mail function is sending out a few hundred or so mail address but keeps hanging when it gets to sending a mail form a certain domain. As the script hangs at this point I can't send anymore mails once the script encounters an address from x domain. What would be the best way to work around this? Why is mail() hanging? How would you suggest incorporating a timeout so that the script continues once mail() has not exited for more than say 5 seconds???? Thanks in advance for your help Scott