SMTP TLS Handshake Error & Login Stuck on nine.testrun.org (Desktop Windows)

Hello Delta Chat Support,

Since 3 days ago, my Delta Chat Desktop (Windows) client has been constantly disconnecting and reconnecting.
Incoming messages works, but outgoing messages fail with the following error:

Error: SMTP connection failure: SMTP failed to connect: tls handshake eof

When I open Advanced → Password and Account and try to recheck or verify settings, the progress bar stays halfway and never finishes.
I have already tried the following steps, but the issue persists:

My account is hosted on: nine.testrun.org.
Other users on the same domain seem to have experienced similar SMTP/TLS connection issues since 3 day ago.

Could you please check if there is a known problem with the SMTP or TLS configuration on nine.testrun.org, or advise me if I should change any client settings?

Thank you for your help!
Best regards,

Which Delta Chat Desktop version do you run? Is it a recent version?

Does creating a new profile work? Could you try creating a new profile, then waiting until it finishes or fails? It should eventually fail, but it may take a long time, so start it and leave it for 10 minutes or so until it reports an error and offers to save the log. If you send the log to delta@merlinux.eu, we can look into it.

If this happens only on some network, e.g. your company network, then it may be that the network is blocking the connection.

Are you by any chance from Russia?