For those of you who are just starting using WHM and are wondering why your attachments are not sent via email, you might consider looking into this article.
The default maximum file size limit that can be sent and received in cPanel is usually 50 MB – set by default. Need to change it to fit your needs? Well, it just takes a few minutes to edit the settings from your WHM account.
Just do the following:
Login to WHM as root
Under Service Configuration, Click “exim Configuration Manager”
Click “Advanced Editor”
Scroll down and Click “Add additional Configuration Setting”
Find “message_size_limit” in pull-down list and choose
Enter limit that you want to change to
Scroll to bottom and click “save”
..that’s it! You have now configured your message size limit.