Thunderbird by default sends attachments using Content-Disposition: inline rather than Content-Disposition: attachment. This happens to cause issue for reviewers using Apple Mail, which gamely displays your patches as body text rather than attachments, making them quite difficult for reviewers to work with. Here’s the fix:
- Open Preferences → Advanced → General → Config Editor.
- Find the key mail.content_disposition_type and set its value to 1.