Thunderbird IMAP "synchronize the most recent x days" not working

Works as designed. Synchronization is about downloading the message bodies for offline use. It's not limiting the download of message headers.

So unchecking the "keep message in all folders" setting essentially renders the "synchronize the most recent x days" option null?

It would prevent Thunderbird from downloading the message bodies for offline use at all. It would still download the message headers.

So a couple scenarios to be clear:

Scenario 1:

• uncheck "keep messages in all folders"
• check "synchronize the most recent x days"
• Result: you will always get ALL headers but no bodies during sync

Scenario 2:

• uncheck "keep messages in all folders"
• uncheck "synchronize the most recent x days"
• Result: you will always get ALL headers but no bodies during sync

Isn't this the same result? I'd really love to know what I'm missing here.

Isn't this the same result?

Yes. To my understanding, if you tell Thunderbird not to download any message bodies, you can't limit the no. of message bodies to be downloaded to 'the most recent x days'. I haven't tried this, so I may be wrong.

Note, even if 'keep messages in all folders' is unchecked, you can still select individual folders for downloading message bodies.

Thanks for taking the time to talk through this with me. I really appreciate it!