clear-code/noapplefile

Prevent storing of the MIME Type "application/applefile".

This add-on prevents mails which Thunderbird sent from being rejected by specific mail servers such as Microsoft Exchange Server 2007.

Detailed information

The cause of this problem is described as follows.

• Some mail clients in Mac OS may attach both the actual file (data fork, e.g., application/pdf) and the meta data of the file (resource fork: application/applefile) in file attaching process for a file.
• Exchange Server 2007 rejects a mail if the mail contains an attached file whose MIME Type is application/applefile.
• If an attached file with the MIME Type unknown to Thunderbird is opened, Thunderbird records the relationship of the extension and the MIME Type of the file. Then if a file with the recorded extension is attached, Thunderbird uses the recorded MIME Type in priority to the MIME Type provided by OS.

As a result, Thunderbird may use the false MIME Type (application/applefile) instead of the actual MIME Type (application/pdf) in a mail, making the mail to be rejected by a recipient who uses Exchange Server.

A widely known workaround for the problem is that remove mimeTypes.rdf in a profile folder of Thunderbird. This workaround resets the recorded MIME types and make Thunderbird use the MIME Type provided by OS.

However, if you receive a mail with an attached file whose MIME Type is "application/applefile", Thunderbird records the false MIME Type into the mimeTypes.rdf and the problem recurs.

Add-on details

This add-on ("No application/applefile") checks for the content of mimeTypes.rdf at start-up. If mimeTypes.rdf contains a problematic MIME Type "application/applefile", the add-on remove the MIME Type.

In addition, if the MIME Type of an attached mail is "application/applefile", the add-on guesses the correct MIME Type of the file from the extension of the file name, and make Thunderbird use the guessed MIME Type.

By doing so, this add-on prevents the problem.

noapplefile's Issues

Compatibility to thunderbird 38.x

The extension used to be a huge relieve, as it renders Thunderbird immune to Apple-Mail's attempts to "poison" the mime-type association (by constantly sending in pdf's as "application/applefile"-FUBAR). Thank you very much for your work so far!

Sadly the extension seems to have stopped working with current Thunderbird 38.x.
As soon as users now open up an "applefile"-PDF, Thunderbird seems to note that down (even saves it within mimeTypes.rdf) and begins to send out that mime-type for his own pdf-Attachments (which ironically leads to problems for Apple Mail, when opening attachments that have been sent by a Thunderbird, that "learned" the wrong mime-type from a mail sent by Apple Mail in the first place).

Is there any chance to make this brilliant extension working again with currently supported Thunderbird releases?

Thank you very much for considering,
kind regards,
DC