PHP Mail Not Functioning when DSO is Enabled (cPanel)

If DSO is enabled with the MPM_ITK module loaded, there is a bug in the entry in the mpm_prefork.conf file.

In the logs you are likely to see unable to set gid=993 or uid=0 (euid=0): forcing real = effective 

You may also get unable to set gid=32009 or uid=32008 (euid=0): system filter

The fix is to add LimitUIDRange 0 40000 to apache mpm_prefork.conf file and restart apache

The danger of this (and in fact enabling PHP Mail at all) is any hacked website on the server will not be stopped from sending SPAM messages and so the mail queues must be closely monitored.