If you or none of your customers aren’t running any mail listings through cPanel, it would be a good idea to disable Mailman.
Go to WHM > Server Configuration > Tweak Settings > Disable Mailman
Catch all can use up many resources and storage space, To disable CatchAll
Go to WHM > Server Configuration > Tweak Settings > Change to :fail:
Tweak Apache to reduce lot of memory.
Change the following settings depending on your server usages.
Save and restart apache now.
Install PHP accelerator (Recompile Apache with eAccelerator)
Compiling Apache with mod_deflate Gzip Module
Turn Off unwanted statistis
Analog Stats, etc.,