E-Mails disappear after a 10 secs and never reappear

I have 5 different mail accounts connected. They all work great except one.
I can see the mails, i.e. in the inbox, for like 10 seconds and then they just disappear.
They are still there when I log into the webmailer. Also, the inbox tells me there are messages left, but just does not display them.

this needs a bit of debugging. what you see in the left sidebar is the result of a query on IMAP, on the right you see a representation of Nextcloud’s message cache.

You can try to find that inbox in oc_mail_mailboxes. Then take its id to find all cached messages in SELECT * FROM oc_mail_messages WHERE mailbox_id=<id>. I would like to know if that result is empty or if it shows that one message.

I’m suffering from the same - notably it only started to appear after I moved from one hoster to another - the new one is manitu. I also see messages toggling between coming and disappearing (i.e. they show fine for a few seconds, then the inbox is empty, then they appear again).

I first cleaned out my installation to avoid it being related to some weird hickup (so removing the mail app, deleting all database entries, notably dropping all nc_nnn_mail tables and removing the entries from nc_nnn_migrations and nc_nnn_preferences and reinstalling the app afterwards. The problem persists.

I checked the database as you suggested Christoph: the messages are there, even when the mailbox appears empty in the app. After around 30sec, the messages are briefly displayed again (together with the notification) and then they disappear. All through this cycle, the database entries didn’t change.

I experimented around by sending emails to myself. The new message was in the database, although it wasn’t displayed yet. Deleting it from the app also made it disappear from the database.

Any help in this matter would be grate. If I can provide more details (e.g. via logs and such), please let me know what you need and I will get it to you.

Thanks for making this app available!