For many years, I have had my Mac Thunderbird 2.x and 3.x configured to auto-forward certain emails via filter to my iPhone.
The problem has been that in spite of being told to send the auto-forwards as "inline" attachements, the iphone sees the '.eml' extension and will not permit viewing/opening of any attachements with ".eml" extensions. I have finally solved this incredibly vexing problem:
Though many believe the solution is to set mail.forward_message_mode to "2", this alone is insufficient, you must also set mail.forward_add_extension to "false"
|mail . forward_add_extension||Boolean
|Add an extension when forwarding a message as attachment.
True: Create attachment name from Subject and add ".eml" extension.
False: Create attachment name from Subject only.
|mail . forward_message_mode||Integer||0: Forward an e-mail as attachment by default.
2: Forward an e-mail inline by default.
These settings are reached in Thunderbird via Preferences -> Advanced -> Config Editor...
Having config'd this way the forwarded mail is now readable, albeit not as nicely formatted, on the iPhone.
[N.B. This method works when selecting a message and choosing to "Forward" it from within Thunderbird. It appears that auto-forwards via Thunderbird filters do not provide the same result and instead produce an email with an .eml attachment--back to the drawing board...]
Hope this helps...