On Wed, May 17, 2023 at 4:04 PM Ralf Becker via dovecot <dovecot@dovecot.org> wrote:

Dovecot 2.3.20 including it's submission server works well with all
sorts of clients, but Outlook.

Outlook works / can connect to Dovecot IMAP service with same
certificate TLS config, but it fails to connect using SMTPs on port 465.
Other clients connect and send mails without problem, also openssl
s_client can connect and reports no problems.

I tried with Outlook Version 365 on Windows 11 (no cloud) and
"Microsoft® Outlook® 2021 MSO (Version 2304 Build 16.0.16327.20200) 64-bit".

I already enabled all submission_client_workarounds and lowered
min_ssl_version from TLSv1.2 to TLSv1, but that changed nothing.

I can see nothing failing in the logs, thought the OL connection wizard
always check IMAP and SMTP together, so it's hard to say what the
problem is.

The same two Outlook version connect without a problem to Postfix
authenticating via SASL to Dovecot also requiring a minimum TLS version
of 1.2.
They just wont connect with Dovecot submission server.

Any ideas what's wrong, or how to debug that further?

Ralf

--

Ralf Becker
EGroupware GmbH [www.egroupware.org]
Handelsregister HRB Kaiserslautern 3587
Geschäftsführer Birgit und Ralf Becker
Leibnizstr. 17, 67663 Kaiserslautern, Germany
Telefon +49 631 31657-0
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Andrzej