If you are facing an error like "not allowed extension file" while you send .eml file in emails, first you need to allow .eml file extensions as follows.
- Login to cPanel server through SSH.
- Copy file /etc/cpanel_exim_system_filter to /etc/cpanel_exim_system_filter_emlallowd.
- Now, login to WHM and navigate to exim configuration. Set default exim filter file as /etc/cpanel_exim_system_filter_emlallowd.
- Remove eml extension from cpanel_exim_system_filter_emlallowd file and Save it.