How to permit .eml email attachments

Introduction

By default, Exim blocks attachments with the .eml extension for security. This article provides the steps to modify the Exim configuration to allow attachments with the .eml extension.

If the Exim Attachments filter is enabled in Exim Configuration manager, the article under Additional Resources, "How to whitelist or allow certain attachments through the Exim filter" will need to be used to allow .eml attachments there as well.

Procedure

1. Log into WHM as the ‘root’ user.
2. Navigate to "Home / Service Configuration / Exim Configuration Manager."
3. Click the "Advanced Editor" tab.
4. Scroll down to the "acl_not_smtp_mime" section.
5. Deselect the "disallowed_filenames_bl" option.
6. Select the "custom_begin_not_smtp_mime" option.
7. Paste the following into the "custom_begin_not_smtp_mime" textbox.

   # Reject inbound mail with potentially dangerous attachments
   # Obfuscation of file names using parameter value continuation evades other filters, but not this one
   
   deny
     log_message = DENY: disallowed \"$mime_filename\"
     condition = ${if match \
     {${lc:$mime_filename}} \
     {[.](ad[ep]|ba[st]|chm|cmd|com|cpl|crt|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|scr|sct|shs|url|vb[se]|ws[fhc])\$}}
     message = Attached file '$mime_filename' has disallowed extension.
   
   accept

8. Scroll down to the "acl_smtp_mime" section.
9. Deselect the "disallowed_filenames_bl" option.
10. Select the "custom_begin_smtp_mime" option.
11. Paste the following into the "custom_begin_smtp_mime" textbox.

    # Reject inbound mail with potentially dangerous attachments
    # Obfuscation of file names using parameter value continuation evades other filters, but not this one
    
    deny
      log_message = DENY: disallowed \"$mime_filename\"
      condition = ${if match \
      {${lc:$mime_filename}} \
      {[.](ad[ep]|ba[st]|chm|cmd|com|cpl|crt|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|scr|sct|shs|url|vb[se]|ws[fhc])\$}}
      message = Attached file '$mime_filename' has disallowed extension.
    
    accept

12. Scroll down to the bottom of the page.
13. Click the "Save" button.

Additional resources

Exim Configuration Manager: Advanced Editor

How to whitelist or allow certain attachments through the Exim filter

How to disable or enable your custom Exim system filter