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Problems sending email with Microsoft Outlook client

  • M

    Hello everyone,

    For a couple of days now I've been having a strange problem with Microsoft Outlook clients.
    I have Mdaemon 14.5.7 installed on a Windows Server 2008 R2 Standard, a configuration that has been working without problems for years.
    Suddenly, for a couple of days now, clients with the Microsoft Outlook client, in versions 2019, 2021 and latest releases, are no longer able to send emails through our server.

    Often the message reported is:

    "The server does not support the specified connection encryption type. Try changing the encryption method. For assistance, contact your mail server administrator or Internet service provider (ISP)"

    On some of these clients, if I change the encryption method, the problem is solved immediately, on others it is not. Also, if I try to configure the same email address on a Thunderbird client, the configuration ends without any problem.

    I have formulated dozens of hypotheses, but without finding a concrete thesis that helps me understand where the cause of the problem could be (server side or client side).

    On my server I have also inserted the domain in the STARTTLS White List that has the problem the most, but without success.

    Has anyone encountered a similar problem?

    Thanks for any suggestions.

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  • A

    MDaemon 14.5.7 is no longer supported, so while I will try to help, my first reccomendation is to upgrade to a supported version of MDaemon.  

    How is Outlook connecting to MDaemon (IMAP, ActiveSync, MDaemon Connector)?

    Check your inbound logs in MDaemon, it should show you the exact error that is occurring.  Once you find a snippet in the log that was generated from a session that returned the error described, post it for us. 

    Also check to make if the clients are using port 993 for IMAP, that you have the encryption set to SSL and if its using port 143 that you have the encrypt type set to STARTTLS.  For SMTP, if you are using port 25,366,or 587, you should be using STARTTLS encryption, if you are using port 465 it should be SSL.

     

    --
    Arron Caruth

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  • M

    @Arron

    hi,

    first of all thanks for your advice.

    - Outlook clients connect both in POP3 and IMAP, even if IMAP is the most used.

    - The error I found in the Mdaemon logs is mainly this:

    Wed 2025-06-18 04:02:25.623: Failed SMTP authentication attempt from <address> for "<e-mail>"
    Wed 2025-06-18 04:02:25.623: --> 535 5.7.8 Authentication failed
    Wed 2025-06-18 04:02:25.677: SMTP session terminated (Bytes in/out: 1119/4133)
    Wed 2025-06-18 04:02:25.677: ----------

    - Finally, regarding the use of ports and their encryption: on some Outlook clients I solved the sending problem by simply setting port 587 and leaving the Outlook setting for choosing the encryption to use in 'Automatic', while in other cases, many I must say, this operation was not successful. The strange thing is that the SMTP reconfiguration was successful with older versions of Outlook, although not always; finally, doing some configuration tests with other clients, Thunderbird for example, there were no problems.

     

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  • A

    When authentication fails,  does Outlook prompt the user to re-enter the password? if you re-enter the password does it start working again?  

    If you edit the profile in Outlook and enter the password again, does it start working?  

    I have seen instances where Outlook, for some unknown reason, starts sending something other than the password as the password.  

    If MDaemon is configured to require full email addresses to authenticate, make sure that Outlook is sending the full email address as the username.  You can find the setting in MDaemon 25.0 under Setup | Preferences | System.  I don't recall for sure where the setting is in MDaemon 14, but I believe it is in the same spot.

    --
    Arron Caruth

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