I think I finally found out what's going wrong.
The problem seems to be that the shared mailbox uses more storage space than the users limit. It looks like dovecot is comparing shared_mailbox.usage + message.size with user.limit.
This was already posted on this mailing list 11 years ago: https://dovecot.dovecot.narkive.com/NMG8xbaD/quota-using-wrong-limits-in-use...
At least I think it's the same problem because after increasing the users quota they were able to save the message. I don't really know why saving worked when we first looked at the issue. It wasn't when I tried today.
Mit freundlichen Grüßen
Markus Bach IT-Administration
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On 4/17/25 12:32, Markus Bach via dovecot wrote:
Oh and I think I didn't mention it: copying and deleting works. It's just saving mail that's affected.
Markus Bach IT-Administration