Note that allowing .eml attachments through the filter can expose the server users to potential malware and phishing! You will want to be aware of this concern before deciding if this change is absolutely necessary.
Make a backup of /etc/system_filter.exim
cp -a /etc/system_filter.exim /etc/system_filter.exim.bak
Note that "eml" is referenced about 4 times in active rules and once in an inactive rule (preceded with a hash symbol, #) in
Each instance will need to be removed from the existing active rules and also just in case you decide to enable the one inactive filter rule, it should also be removed from there.
Either manually edit /etc/system_filter.exim and remove all references to "eml" (you'll have to remove the pipe character "|" that follows the eml entry, too), or use sed or perl to accomplish this.
sed -i 's/eml|//g' /etc/system_filter.exim
Use the following command to ensure that all references to the .eml entry are removed:
grep -o 'eml|' /etc/system_filter.exim
Note that you could have skipped Step 1 if you chose to use sed instead of editing the file manually since it allows you to specify the extension to use for a backup copy of the file to be made prior to the edits it will apply. The following will make the file "/etc/system_filter.exim.bak".
sed -i.bak 's/eml|//g' /etc/system_filter.exim
Restart Exim via SSH as the root user like so:
service exim restart
Or restart exim service via the panel GUI
DA Control Panel --> Admin Level --> Service Monitor --> (exim) Restart
If you require assistance with implementing the changes described here on your server, please feel free to open a ticket with your 24/7 KnownHost support team and we'll be glad to help! :)