PHP problem — comments being mailed?

Hi all-

My WordPress install is set up to send me an e-mail whenever a new comment is posted on a post; however, some services on my host server (including e-mail) went down this morning and when we brought them back up, this feature no longer worked. E-mail in general is working, but WordPress-generated messages don’t go through.

I am having a similar problem with automatically-generated e-mails from PHPBB on the same server, so I am assuming the problem is with PHP. However, my host doesn’t really support PHP issues, so I need to figure out at least the outlines of the problem myself. Unfortunately, I’m kind of a dummy about it. Does anyone know what PHP modules WordPress uses for to generate its automatic mail messages? That would get me started, anyway. Thanks in advance!