Mailbox list Error on new installation

A new installlation with 2 email accounts. The second account works fine, but the first throws up a periodical error: “[IMAP] Cannot open folder “/mailboxlist”. (NO [SERVERBUG] Internal error occurred. Refer to server log for more information. [2022-09-22 17:47:16] (0.001 + 0.000 secs).)”

Despite that, emails arrive and can be sent, and test messages are sent and received ok.

Help, please!

Have you tried removing the problem account and re-adding it?

I hadn’t, but have now done so. Same problem, unfortunately. Odd: I have the same account / email address set up on EmClient on 2 other devices with no problems.