PHP mail() stopped working, sendmail error

Error logs from cPanel shows these messages when trying to email using php mail() .

var_dump(error_get_last()) returns NULL

tail /var/log/maillog shows:

Any idea?

 

That looks like a logging-error - does the email actually get sent?

 

How big is your log file? A little search shows others that had similar problems with solutions ranging from taking care of a huge log file to a file permission issue.

 

What log file?

ls -l /var/log/maillog
-rw------- 1 root root 766100 Dec 27 04:20 /var/log/maillog

ls -l /var/log/messages
-rw------- 1 root root 15940517 Dec 27 04:20 /var/log/messages

 

This fixed it:
chmod 4755 /usr/sbin/exim