Instable connection to local hosted IMAP server

[Geryishere]

Steps to reproduce

1. Nextcloud is installed on own LXD container.
2. I use XEAMS installed on another LXD container as local hosted IMAP server .
3. Connection between Nextcloud Mail as client and Xeams as local host IMAP server is established without problems.
4. SMTP Server connection is WEB.de SMTP server.
5. After synchronising the email account on nextcloud mail with local IMAP, the IMAP server connection breaks down shortly after.
6. In order to fetch the emails again, synchronising needs to be done manually (by reloading nextcloud mail).
7. Then however, the IMAP connection breaks down again.

Expected behavior

The connection between Nextcloud Mail as email client and XEAMS used as local hosted IMAP server should be stable without interruptions.

Actual behavior

"reqId": "tXsefM4Jl5KSf6J64r6C",
"level": 2,
"time": "2024-09-28T12:07:41+02:00",
"remoteAddr": "77.109..*",
"user": "Gery",
"app": "mail",
"method": "POST",
"url": "/apps/mail/api/mailboxes/31/sync",
"message": "Mailbox UID validity changed. Wiping cache and performing full sync for 31",
"userAgent": "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36",
"version": "28.0.9.1",
"data": {
"app": "mail"
},
"id": "66f7d5ce65aca"

[PHP] Error: Undefined array key "uidvalidity" at /var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php#4066
POST /apps/mail/api/mailboxes/95/sync
from 77.109..* by Gery at 28 Sept 2024, 11:32:53

"reqId": "pJdPemv2GN1DcQAjq51W",
"level": 3,
"time": "2024-09-28T11:32:53+02:00",
"remoteAddr": "77.109..*",
"user": "Gery",
"app": "PHP",
"method": "POST",
"url": "/apps/mail/api/mailboxes/95/sync",
"message": "Undefined array key "uidvalidity" at /var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php#4066",
"userAgent": "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36",
"version": "29.0.7.1",
"data": {
"app": "PHP"
},
"id": "66f7cdb1a0f34"

Mail app version

3.7.8

Mailserver or service

XEAMS hosted locally in the same network as nextcloud

Operating system

Ubuntu 22.04.5 LTS on LXD container

PHP engine version

PHP 8.3

Web server

Nginx

Database

PostgreSQL

Additional info

The same problem exists with Nextcloud Mail app in other Nextcloud versions (Nextcloud 27 and 28) running Apache2.

[ChristophWurst]

Mailbox UID validity changed.

This is a very rare event. We'll have to check if the code is still doing the right thing.

[Geryishere]

This event happens for ALL locally self hosted IMAP (mail)sever within the same network as Nextcloud. Only external (commercial) IMAP mailserver such as Google, GXM etc. are not affected.