Overview
Some email clients (Gmail, Outlook, iPhone Mail) send forwarded messages in a format that may cause Mailman mailing lists to deliver them as attachments instead of inline messages.
This guide explains how to adjust a Mailman list so forwarded emails are delivered normally.
Symptoms
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A list member forwards an email to the list
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Everyone receives an email with the forwarded content as an attachment (often
message.htmlormessage.rfc822) -
The list itself appears to be working, but forwards are not displayed inline
Cause
Forwarded messages from some email clients use MIME types that Mailman does not pass through unless explicitly allowed.
By enabling content filtering and allowing the correct MIME types, Mailman can unwrap and deliver the message inline.
How to Fix It (Per List)
Follow these steps for the affected mailing list:
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Log in to cPanel
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Go to Mailing Lists
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Click Manage next to the list
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Open Privacy Options
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Click the Content Filtering subsection
Update the following settings:
1. Enable content filtering
2. Add allowed MIME types
Under pass_mime_types, enter:
3. Disable conversions
Set:
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Scroll down and click Submit Your Changes
Why This Works
Certain forwarded messages are wrapped using the MIME type message/rfc822.
Allowing this MIME type tells Mailman to accept the forwarded message and unwrap it instead of attaching it.
This change applies only to the specific list — not to the server or other domains.
Optional: Test the List
Ask a member to forward an email again.
If everything is configured correctly, the forwarded content will now appear inline.