Every time I go on holiday with my Samsung tablet with K-9 installed, synchronisation with K-9 and Thunderbird on my desktop computer is non existent as far as I can see
I open up K-9 and all the emails from my last holiday are there, and they do not auto delete even though they are no longer in Thunderbird.
Nothing seems to synchronise in either direction, or very little perhaps.
I have IMAP for my mail account (server is imaps.aruba.it) and I’m seeing something very similar. Emails that I delete or archive from my phone (Thunderbird) are still shown as unread in the inbox when I log in through the webmail. Synchronisation is active in the settings. Is there anything specific I could check?
Edit: Thunderbird 12.1 on Android 15 (Fairphone 5)
That sounds like something I experience with Thunderbird without regards to whether I am using K9 or not. Thunderbird seems to be lazy about synchronizing move operations to the server. It normally eventually does synchronize if I wait 10+ minutes. It probably happens more quickly if you click the Get Messages button. I think this might be specific to the type of IMAP server—Thunderbird seems to synchronize folder moves for Office365 accounts almost instantly whereas my Courier IMAP exhibits the behavior you are describing for example. Maybe Thunderbird is tripping up over itself when it synchronizes both “mark read” and “move” operations at the same time so it ends up almost always scheduling a retry on the “move” operation. K9 seems not to have this issue. If I execute a move in K9 it shows up in Thunderbird almost instantly regardless of which server I am using.
It does sound to me like you have manual fetch turned on instead of polling or push. I’d enable at least polling on the tablet for the main folders you use and leave it off for auxiliary ones. But then you have to remember to manually synchronize the auxiliary folders when you need one.