I'm composing emails in Thunderbird. When I attach png images by dragging to the header region, they are attached as

Content-Type: image/png;
Content-Transfer-Encoding: base64
Content-Disposition: attachment;

When I attach them inline by dragging into the body, they are attached as

Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: base64
Content-ID: <part1.00030206.09040704@my.sending.domain.com>

The latter displays fine for the recipient if they are using Thunderbird, or via the gmail web interface. However, I've had complaints from OSX Mail.app users that they can only see a text file <Mail Attachment.txt> full of nonsense. They have to save the file and rename it to *.png.

Also kmail is confused by this attachment, although it seems to get some information from the attachment: enter image description here

Should the attachments not be sent as text/plain? (However, it's interesting that Gmail understands it.) If so, then how can I make Thunderbird send inline attachments as the proper mime type?

  • Weird. I am using TB 24 on Windows and inline attachments are image/jpeg and base64. What OS are you using? Any extensions installed?
    – Paul
    Oct 22 '13 at 5:46
  • @Paul Linux/(K)Ubuntu (and TB 24). I do have a few add-ons installed, but I just tested in safe mode and get the same problem. Do you also see the same thing with png (not jpeg)?
    – Sparhawk
    Oct 22 '13 at 5:49
  • Yep: Content-Type: image/png; name="fbigiaca.png" Content-Transfer-Encoding: base64
    – Paul
    Oct 22 '13 at 5:52
  • @Paul Interesting. At least this suggests it is a problem with (my) Thunderbird then. (Also, it's strange that Gmail via the web is okay with it.)
    – Sparhawk
    Oct 22 '13 at 5:53
  • Ah, hang on, I did it with TB linux, and got the same as you.
    – Paul
    Oct 22 '13 at 5:55

Thunderbird downloaded from the website works fine, so it looks like it's a bug introduced in the Ubuntu packages. I've filed a bug here.

To follow up, the Arch packages do not contain this bug, it's definitely something introduced in Ubuntu's packaging.

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