So after actually getting a complaint about it, I finally got fed up with Thunderbird sending text file attachments as inline attachments. I’d already been annoyed at GMail displaying things I sent myself inline, making it hard to copy diffs (because the amount of whitespace at the end needs to be exactly right) or easily save files.
Here’s how to tell Thunderbird to always send attachments as attachments, instead of inline:
- Open the Thunderbird Preferences (this is under “Preferences” in the Edit menu, or “Options” in the Tools menu, depending on your OS).
- Go to the Advanced section, and the General tab on there.
- Click the Config Editor button on there.
- Enter mail.content_disposition_type in the filter box.
- Double-click the only item in the list (with the exact name mail.content_disposition_type, obviously), and enter 2 as its value (instead of the 0 it’s on originally).
- Close the Config Editor with the [x], and close the Preferences with [OK].
You’re now done. Thunderbird will now send plain text files as an attachment. Any other non-binary files will still be sent inline. If you want all your files to be ‘real’ attachments rather than inline attachments, set the pref to 1 instead. Tip-of-the-hat to Marco for the tip about using 2 instead of 1.