You may receive a bounce back message saying “Message size exceeds maximum permitted” on sending an email greater than the size defined in the exim configuration. On a cPanel server, the message size limit is 50MB by default.
In order to raise the message size limit, you need to edit the exim configuration file either manually located at /etc/exim.conf OR from WHM >> Exim Configuration Editor > Advanced Mode and at the very start of the file, add the following line:
message_size_limit = 100
Save the file and restart the exim service.
# service exim restart
This will increase the message size to 100MB. You can verify the new size by executing the following command:
# exim -bP | grep message_size_limit