Its because you have mail home and mail location/mail path pointing to same place, which is a common misconfiguration.

Easiest fix for you is probably to configure sieve path to something like ~/sieve (no leading dot) to avoid ~/.dovecot.sieve dir from being seen as maildir folder.

Aki

 On 14/04/2026 15:59 EEST 87auteur-niobium--- via dovecot
 <[1]dovecot@dovecot.org> wrote:


 Hi folks,

 I'm seeing "INBOX.dovecot.sieve" listed on the response of the IMAP LIST
 command, but attempting to select the mailbox fails with "Internal
 server error occurred. Refer to the server log for more information".
 I assume INBOX.dovecot.sieve is an internal/system folder that shouldn't
 be on the LIST response.
 Is this a known issue? If it is, is it being tracked anywhere (I don't
 see an "Issues" tab on GitHub for Dovecot Core)?
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