Unable to load mailbox

Steps to reproduce

1. enter account information
2. Account is created, logon succeeds
3. Account creation creates an error when loading the mailbox

Expected behavior

loading of mailboxes succeeds

Actual behavior

loading of mailboxes failes

Mail app version

4.0.0

Mailserver or service

Own iMAP (courier-imap-ssl) on Nextcloud server

Operating system

OpenSuse

PHP engine version

PHP 8.2

Web server

Apache (supported)

Database

MariaDB

Additional info

Connection to my own IMAP used to work - with around 3.2.x it stopped working, however, only with my account.
For the accounts of my wife and daughter the mail app still works (same server, only different mailboxes)

If I recreate my account, it cannot be added and fails with provided log entry after successful account creation / logon.

There are no errors in the SysLog of the server. (Courier mentions the login, no other report nor error)

NextCloud Log:
{"reqId":"KjZvNc6nsrgJ3iXLGt5A","level":3,"time":"2024-09-17T14:43:05+00:00","remoteAddr":"192.168.1.5","user":"quippy","app":"mail","method":"GET","url":"/nextcloud/apps/mail/","message":"Could not load account mailboxes: IMAP error synchronizing account 27: IMAP error reported by server.","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:130.0) Gecko/20100101 Firefox/130.0","version":"30.0.0.14","exception":{"Exception":"OCA\Mail\Exception\ServiceException","Message":"IMAP error synchronizing account 27: IMAP error reported by server.","Code":0,"Trace":[{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/Service/MailManager.php","line":134,"function":"sync","class":"OCA\Mail\IMAP\MailboxSync","type":"->","args":["*** sensitive parameters replaced "]},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/Controller/PageController.php","line":156,"function":"getMailboxes","class":"OCA\Mail\Service\MailManager","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":208,"function":"index","class":"OCA\Mail\Controller\PageController","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":114,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/App.php","line":161,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/Route/Router.php","line":302,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/srv/www/htsdocs/nextcloud/lib/base.php","line":1001,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/index.php","line":24,"function":"handleRequest","class":"OC","type":"::"}],"File":"/srv/www/htsdocs/nextcloud/apps/mail/lib/IMAP/MailboxSync.php","Line":109,"Previous":{"Exception":"Horde_Imap_Client_Exception_ServerResponse","Message":"IMAP error reported by server.","Code":0,"Trace":[{"file":"/srv/www/htsdocs/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php","line":4319,"function":"_getLine","class":"Horde_Imap_Client_Socket","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php","line":4243,"function":"_sendCmdChunk","class":"Horde_Imap_Client_Socket","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php","line":3903,"function":"_sendCmd","class":"Horde_Imap_Client_Socket","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php","line":3330,"function":"_getMyACLRights","class":"Horde_Imap_Client_Socket","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/IMAP/FolderMapper.php","line":118,"function":"getMyACLRights","class":"Horde_Imap_Client_Base","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/IMAP/MailboxSync.php","line":107,"function":"fetchFolderAcls","class":"OCA\Mail\IMAP\FolderMapper","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/Service/MailManager.php","line":134,"function":"sync","class":"OCA\Mail\IMAP\MailboxSync","type":"->","args":[" sensitive parameters replaced ***"]},{"file":"/srv/www/htsdocs/nextcloud/apps/mail/lib/Controller/PageController.php","line":156,"function":"getMailboxes","class":"OCA\Mail\Service\MailManager","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":208,"function":"index","class":"OCA\Mail\Controller\PageController","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":114,"function":"executeController","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/AppFramework/App.php","line":161,"function":"dispatch","class":"OC\AppFramework\Http\Dispatcher","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/lib/private/Route/Router.php","line":302,"function":"main","class":"OC\AppFramework\App","type":"::"},{"file":"/srv/www/htsdocs/nextcloud/lib/base.php","line":1001,"function":"match","class":"OC\Route\Router","type":"->"},{"file":"/srv/www/htsdocs/nextcloud/index.php","line":24,"function":"handleRequest","class":"OC","type":"::"}],"File":"/srv/www/htsdocs/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php","Line":4620},"message":"Could not load account mailboxes: IMAP error synchronizing account 27: IMAP error reported by server.","exception":{},"CustomMessage":"Could not load account mailboxes: IMAP error synchronizing account 27: IMAP error reported by server."}}

Start in apps/mail/lib/IMAP/MailboxSync.php around sync and FolderMapper.php around fetchFolderAcls, following the logged call into Horde_Imap_Client_Socket. Reproduce the account-specific failure with Courier IMAP and inspect the server response. Done means the affected mailbox loads successfully without the reported synchronization error.