PHP Mail function stopped working

[TheClicker]

Yesterday before 2:30, we were receiving email from the servers just fine. The same code today doesn't work. We haven't received an email for almost 24 hours now from the server.

I've looked at every different way we send email:

Newsletter program: works with SMTP send, but not PHP mail send (it has the option)
CGI Forms: work
PHP Mail pages - nothing.

I've gone through everything I did yesterday, and I can't find anything that I could have changed that could possibly be making this type of problem occur. After 2:30, I picked up my kids from school, created two new pages on the domain that had nothing to do with mail, and got a CSR for a new SSL cert. Our server admin doesn't remember doing anything either.

What could possibly be causing this?

TIA
Clicker

[jatar_k]

Welcome to WebmasterWorld TheClicker,

well something definitely changed

what os is the server running?
were any upgrades done to anything at all on the server (be it mail or web)?
have you tried some basic mail calls in a simple php test script to try and isolate the issue?

[StupidScript]

Has the new cert been installed?