PHP Possible Issue with Microsoft Exchange?

PHP sends mail to exhange but no mail is ever sent

[5x54u]

Has anybody had an issue while using PHP and PHPMailer script that when the email is sent to Microsoft Exchange server; the email is never sent?

Background:

Have been hosting on IIS Box for 4 years using PHP and the same form submission handler that utilizes PHPMailer that sends the mail to SMTP which is handled by Microsoft Exchange.

Friday night around 10 the bug began where when a form submission was received, the PHP script handled everything properly and recieved no errors; mail was sent to queue but it never is received by recipient. All indications show no sign of an error?

To solve the problem I had to redirect to a regular non-exchange mail server to fix the problem?

Host is telling me nothing has changed on or been updated to exchange server and is pushing the issue on to PHP.

FYI - I wrote an asp script to test the exchange server and it worked fine and recipient did recieve mail.

Anyone heard of something like this?

[coopster]

What changed? If not something on the server, was it the number of emails attempted to send at any given time, etc. Something had to have changed ...

[5x54u]

Nothing changed according to host. I believe him he is related to me.

Created new IIS relay on a separate box with identical config/settings/paths and pointed to that box - no issues. Is it possible something became corrupt that would only affect PHP? The asp worked with no issues on problem IIS relay box.

Thank you for input.