This one’s here because I spent the better half of an hour troubleshooting this for a customer.
Fatal error: Out of memory (allocated 47448064) (tried to allocate 13472326 bytes) in
/usr/local/cpanel/3rdparty/lib/php/Net/SMTP.php on line 821
Sending messages through Webmail with attachments larger than 10MB.
If you’ve stumbled upon this post as a result of furious internet searching for similar issues, you’ve likely found thousands of posts regarding the error indicating the problem lies in the php.ini file of cPanel or Horde. While the PHP memory limit for cPanel and Horde are defined in their own php.ini, this does not actually alleviate the error seen here. cPanel itself will actually kill off applications consuming more than what is defined in Tweak Settings.
WHM (as root) ->Tweak Settings > The maximum memory a cPanel process can use before it is killed off.
Change this to 512M or 0 to disable memory limits all together.