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Outlook cannot log in to the mail server account deployed in Stawart.

StephenJose_Dai 0 Reputation points
2025-12-13T06:49:08.25+00:00

I deployed a mail server using Stawart. I can log in to my account normally using 163, Thunderbird, Tencent, and the email client that comes with my Android phone. However, when I try to log in with Outlook, it keeps giving me an error. I've tried using both my regular password and the application password, but I get the same error each time. I don't know what the problem is!

I've looked at similar articles, but it seems no one has solved this problem. What should I do? Can you help me?

我使用Stalwart部署了一个邮件服务器，我使用163、雷鸟、腾讯以及安卓手机自带的邮件客户端都可以正常登陆我的账号，但是当我使用Outlook登录它时，它一直报错，我尝试使用了普通密码和应用程序密码，都会得到相同的报错，我不知道这是什么问题！

我查看了相同的文章，似乎都没有任何人解决了这个问题，我该怎么做？可以帮助我吗？

{"SessionId":"4ad192c3-ebde-d743-bfd1-2e341ac4f611","Timestamp":1765602851541,"Error":"INVALIDCREDENTIALS TEMPORARILYUNAVAILABLE"}

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  1. Emmanuel Santana 33,875 Reputation points Independent Advisor
    2025-12-13T08:55:47.4933333+00:00

    Hello. Outlook is never getting past the TLS handshake. Authentication is not even starting:

    DEBUG TLS handshake error (tls.handshake-error) reason = "Connection reset by peer (os error 104)"

    When this happens, Outlook surfaces INVALIDCREDENTIALS / TEMPORARILYUNAVAILABLE because it cannot establish a secure session. It uses a generic auth error even when TLS fails. That’s expected behavior.

    Can you please check your Stalwart configuration file (mail.toml or equivalent) and confirm whether TLS 1.2 and TLS 1.3 are enabled, with older versions such as TLS 1.1 or below disabled? Also, if you have explicitly defined cipher suites, can you temporarily comment them out to let Stalwart use its default modern cipher list, or verify that the configured ciphers support forward secrecy?

  2. Emmanuel Santana 33,875 Reputation points Independent Advisor
    2025-12-13T10:25:00.1933333+00:00

    Thanks for the update. In that case, the TLS protocols and cipher suites themselves are fine.

    You are running IMAP on port 993 while Implicit TLS is disabled. Port 993 requires implicit TLS, meaning the TLS handshake must start immediately when the client connects. Outlook expects this and will abort the connection if it does not happen, which matches the TLS handshake reset shown in your logs.

    Enable Implicit TLS on the IMAP listener bound to port 993, or alternatively move the listener to port 143 and use STARTTLS instead. Do not mix port 993 with explicit TLS.

    Also note that the listener is currently bound only to [::]:993 (IPv6). For compatibility, especially with Outlook, you should also bind 0.0.0.0:993 to allow IPv4 connections.

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