How to limit the overall size of emails

Issue :

How can the overall size of an email including attachment, encoding etc. be limited to a pre-defined value?

Solution :

This can be done in the following way :
Go to WHM >> Main >> Service Configuration >> Exim Configuration Editor
In the first box where you can type ( right below where you see ‘#!!# cPanel Exim 4 Config’ ), add the following directive :

message_size_limit = 100M

This will limit the overall size of the message to 100Mb