Thunderbird for Android Community Forum

I just installed Thunderbird for Android on my Pixel phone for the first time. I have used Thunderbird on my desktop PC for many years, so I am very familiar with Thunderbird in general. I used the "Export for Mobile" feature on my desktop installation, to import my account settings into the Android installation.

For the most part, Thunderbird for Android works great, as I would have expected. However I am seeing a problem which appears (to me) to be a bug. When I compose and send an email on my phone, and then look in the "Sent" folder on the phone, the email that I just sent shows up there. But only on the phone. If I open Thunderbird on my desktop PC and look at the Sent folder there, the email that I sent from the phone is not there. Apparently, it only gets placed in the phone's Sent folder, but it does not get copied to the email server.

A few other details: -- I use Thunderbird on 2 different desktop systems, a PC and a Mac. When I send email from either of those, that email DOES show up in the Sent folder on the other system. Emails that are sent from either desktop system also show up in my phone's Sent folder. So I know that the Thunderbird desktop application does upload the message to the email server's Sent folder correctly. But Thunderbird for Android does not upload its sent emails.

-- I don't know if it matters, but my email server is Microsoft 365, hosted by GoDaddy.

-- As far as I can tell, the most obvious setting for this is the "Upload sent messages" checkbox, which can be found in the "Sending mail" section of "Account settings" in the Thunderbird Android settings. This checkbox IS IN FACT turned on. I could not find any other settings which could possibly affect the copying of sent messages up to the email server's folders.

Is this a bug? Any ideas what might be causing this? Thanks for any help.