managesieve-login auth silently failed

Steps to reproduce

1. Make sure you have a wrong password for sieve server
2. Set OOO message on the availabilty page and save
3. A notification claims the OOO message has been saved, but it doesn't (it could not with a wrong password)

For some reasons, when the LDAP password is updated on the Active Directory side, the provisioned mail account on nextcloud sometimes seems to keep an old password or to loose the sieve password configuration.
On the imap/sieve server (dovecot) mail.log, we can see this error :

2026-03-03T00:00:51.335401+01:00 imapsrv dovecot: managesieve-login: Disconnected: Connection closed (auth failed, 1 attempts in 2 secs): user=myuser, method=PLAIN, rip=1.2.3.4, lip=4.3.2.1, TLS, session=PhfPjhJMpJrU6gOT

But on the client side, there is no error, the OOO is apparently saved, letting the user believe he can go on holidays !

Expected behavior

An error message should be thrown on nextcloud when the user save the OOO message, if the sieve auth failed.

And the provisioned mail account (working on IMAP and SMTP) should keep the sieve password up to date (I cannot reproduce that myself, but several users are experiencing similar problems)

Actual behavior

From the user side, all is good, the OOO is apparently saved, but it's not, because of sieve auth failed.

Mail app version

5.7.2

Nextcloud version

33.0.0

Mailserver or service

dovecot

Operating system

debian

PHP engine version

PHP 8.3

Nextcloud memory caching

apcu

Web server

Apache (supported)

Database

MariaDB

Additional info

No response