Error: Invalid Mailbox List when festching mails from 1 of 12 Boxes

[volvisti]

Hi,
just saw, that there was a closed entry #186.

Since, I don't know when, we are getting errors when fetching mails from one special mailbox.
All others (11 Boxes) are running fine.

By default, only unread mails of the last 3 days should be fetched.
So I had the idea of tagging only one Mail as unread, checking what happens.
And... altough there is only one unread mail in the box we are still getting the following error:
[2025-10-28 15:24:56] Error: Invalid mailbox list: @strato.de; Invalid mailbox list: @t-online.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @decentraland.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @shein.com; Invalid mailbox list: @strato.de; Invalid mailbox list: @paypal.de; Invalid mailbox list: @playstation.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @opensea.io; Invalid mailbox list: @amazon.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @amazon.de; Invalid mailbox list: @strato.de; Invalid mailbox list: @strato.de; File: /www/html/overrides/webklex/php-imap/src/Connection/Protocols/LegacyProtocol.php (103)

So I tried out having no unread mails in the box.
Unfortunately it's the same.

At the end of the fetch-emails.log there is the entry:
[2025-10-28 15:47:16] Fetching finished
PHP Fatal error: Uncaught ErrorException: PHP Request Shutdown: Invalid mailbox list: @dhl.de (errflg=3) in Unknown:0
Stack trace:
#0 [internal function]: Illuminate\Foundation\Bootstrap\HandleExceptions->handleError(8, 'PHP Request Shu...', 'Unknown', 0)
#1 {main}
thrown in Unknown on line 0

Has anybody an Idea what to do to get rid of the error?

Here is the setup:
Program-version: 1.8.190
DB: Mysql (10.6.7-Maria-DB)
PHP-Version: PHP 8.2.28

Any help is welcome