SMTP - Outlook 2019 sends wrong TLS cipher list

Maxvatar 11 Reputation points
2022-10-14T08:10:41.693+00:00

Hello all,

from yesterday 13.10.2022 my Outlook (ver. 2209 Build 16.0.15629.20200 64bit, on Windows 10) doesn't sends emails via SMTP server, which is based on Postfix v.3.5.13.
The error message is 0x800ccc1a, which occurs when there is an issue about Secure Socket Layer (SSL). Indeed, there is log on server side, that a SMTP client tries to connect from my IP and that it sends weird list of supported ciphers:
TLS cipher list "aNULL:-aNULL:HIGH:MEDIUM:+RC4:@STRENGTH:!aNULL"

I surely know there was no change on server side - I'm one of two administrators of the server. Nevertheless there was a Windows and BIOS updated installed on my laptop on 12.10.2022 in the evening.

I tried to switch from SSL/TLS to STARTTLS (with proper port), but the error is the same.

I switched on the logging in Outlook, but there is no reasonable logging for SSL part of connection. The log contains only this:
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Port: 587, Secure: TLS, SPA: yes
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Finding host
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Connecting to host
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Connected to host
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 220 mail.xxxxxxx.zz ESMTP Postfix (Debian/GNU)
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): [tx] EHLO MaxNB4
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-mail.xxxxxxx.zz
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-PIPELINING
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-SIZE 30720000
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-VRFY
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-ETRN
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-STARTTLS
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-ENHANCEDSTATUSCODES
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-8BITMIME
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-DSN
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250-SMTPUTF8
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 250 CHUNKING
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Securing connection
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): [tx] STARTTLS
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): <rx> 220 2.0.0 Ready to start TLS
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Securing connection
2022. 10.14 09:37:18 SMTP (mail.xxxxxxx.zz): Disconnected from host

Does anybody solve this issue ?

Thank you in advance.
Best regards
MaX

Outlook Management
Outlook Management
Outlook: A family of Microsoft email and calendar products.Management: The act or process of organizing, handling, directing or controlling something.
4,895 questions

2 answers

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  1. AntonioFontes-0748 1 Reputation point
    2022-10-14T13:13:48.677+00:00

    Hi,
    I don't know if it is related but since yesterday, many of our users report Office app connections to SharePoint being broken, showing SSL errors.

    We started debugging the situation and resorted to packet capture. First signs indicate all Office clients apps are dropping the connection (TCP RST sent by the client to the server) immediately after they receive a certificate request from our servers. We suspect that the client has lost its ability to choose the correct user certificate and thus triggers the connection reset.
    We can still connect to this SharePoint using a web browser (also requiring client authentication, with the same certificates being accepted) so our ongoing hypothesis is that something was modified in how Office apps initiate TLS connections. I am trying to locate a changelog or alike to understand what exactly was changed in the latest Windows / Office update.

    Best regards,
    A

  2. starbuck3000-3037 1 Reputation point
    2022-10-14T14:06:25.317+00:00