Problem with Server Connection for Mail Merge Email

I try to configure the server connection for the Mail Merge Email but when I test the server connection with the “Test Settings” button the connection fails. I always get en error dialog stating that establishing network connection failed and Find outgoing mailserver failed. Additionally there is a python stack trace:

LibreOffice could not connect to the outgoing mail server. Check your system's settings and the settings in LibreOffice. Check the server name, the port and the secure connections settings
--
<class 'imaplib.IMAP4.error'>: b'* BYE Autologout; idle for too long', traceback follows
  File "C:\Program Files\LibreOffice\program\mailmerge.py", line 309, in connect
    self.server = imaplib.IMAP4(server, port)
  File "C:\Program Files\LibreOffice\program\python-core-3.8.14\lib\imaplib.py", line 201, in __init__
    self._connect()
  File "C:\Program Files\LibreOffice\program\python-core-3.8.14\lib\imaplib.py", line 249, in _connect
    raise self.error(self.welcome)

I double checked the settings for my server and I use the same settings on the same machine in my email client.
Can anyone help me in finding the cause for this error.

OS is Windows11 an LO is 7.4.2.3 (x64)

grafik

Have you tried clicking on the Server Authentication… button?

But you never mentioned which those settings were (at least the server and port (no personal information: user name and password, indeed), which might reveal e.g. that your server is not an SMTP server).

Sure I also entered the parameters for the Server Authentication dialog.

I’m using smtp.strato.de on port 465 secured with TLS/SSL. The Authentication for the outgoing is the same as for the incoming server. The incoming server is imap.strato.de on port 993 and it is an IMAP server.