Open Radar

 
If a MailKit extension crashes, Mail does not re-load it, and it is essentially ‘disabled’ for the current run of Mail (unless disabled/reenabled manually).

Steps:

1. Build, run and enable the included extension project, which is a modified version of Apple’s sample MailKit extension.
2. View a message, and confirm the extension is active by looking for the puzzle icon in the message headers
3. Switch to another message a couple of times - this will trigger the extension to crash. The puzzle icon will disappear from the message headers.
4. Open Mail’s Extension preferences - the extension is still shown as enabled.
5. Disable, then reenable the extension (or, relaunch Mail), this activates the extension again (can be confirmed by looking for the puzzle icon in the headers)

It would be expected that Mail would simply re-load the extension again (similar to how a crashed Login Item gets relaunched), or at least indicate the extension is disabled more prominently (instead of just looking for the puzzle icon, which has esoteric meaning in this context), either via some messaging to the user, or at least showing the extension as being disabled in the Extension preferences.

Why this is bad UX:

While it’s preferable not to crash at all, sometimes crashes just happen™️. If Mail doesn’t automatically reload a crashed extension, it is effectively disabled, which means it’s not doing what the user expects it to do, all without any clear indication to the user of this. The user will not automatically know they need to relaunch Mail or need to disable/reenable the extension in the preferences.

Tested on macOS Sonoma 14.4 Beta (23E5196e)