This is a gmail imap account? And what version of Thunderbird for Android?

I use four different email addresses/accounts. One is Gmail, the other three use servers operated by a private company, Pair Networks. All four accounts are set up as IMAPs in Thunderbird version 141.0 (64-bit) on my laptop, and I exported them to Thunderbird for Android version 10.1, using the "Export to Mobile" QR code. As far as I can tell I have this problem on all four email accounts.

I've just run a test: it doesn't happen on the Gmail account, only on the Pair Network accounts.

So https://www.pair.com/ ? Did it ever work correctly with these three accounts?

To be honest, I can't say. Looking into this yesterday, however, I noticed that there's something strange going on with the file structures for the Pair accounts. They have a "webmail" setup, where I can do email on a website. On that site, I see that the inboxes have subfolders for drafts, sent, junk, and trash, and in some cases there are duplicate folders for sent, trash, and junk that are separate and at the same level of the file structure as the inbox.

Those separate folders don't appear in Thunderbird. In fact, the Thunderbird app won't let me create them. When I send an email from a Pair account using my laptop, it ends up in the separate "sent" folder on the Pair Webmail server and in the "sent" folder in Thunderbird on both my laptop and my Android phone, but when I send one from one of those accounts on my phone it simply disappears--although it does get sent.

To make things more confusing, on one of the Pair accounts Thunderbird sets up the file structure differently than it does on the other two. This doesn't affect how it works, though: sent emails are still saved and findable when they're sent from my laptop and they disappear altogether when they're sent from my phone.

I just noticed something else: On my phone, but not on my laptop, when I delete a file on any of my Pair accounts, it disappears altogether. It doesn't end up in either of the two trash folders on the phone associated with that account, nor on the trash folders on my laptop.

... I think I'm going to have to go back to Gmail on my phone ... Too bad.

I've just verified that I don't have these problems with my Pair Networks accounts using the Gmail app for Android ... so, unfortunately, I'm switching back to Gmail. Let me know if you figure out what's going on with Thunderbird for Android, and thanks for trying.