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Outlook fails to send an email: SASL authentication failure. On Plesk for Linux

Renan Poss Moreira
Updated
Plesk for Linux kb: technical ABT: Group B

Applicable to:

  • Plesk for Linux

Symptoms

  • On attempt to send an email via Microsoft Outlook, the login/password prompt appears and does not accept credentials.
  • The warning below can be found in the /var/log/maillog:

    CONFIG_TEXT: mail.example.com postfix/smtpd[17318]: warning: SASL authentication failure: realm changed: authentication aborted

Cause

Current implementation of a DIGEST-MD5 authentication in libsasl2 library is incompatible with Microsoft Outlook.

Resolution

  1. Login to the server via SSH.

  2. Back up the file:
    For CentOS/RHEL-based distributions:

    # cp /usr/lib64/sasl2/smtpd.conf /usr/lib64/sasl2/smtpd.conf.bak

    For Debian/Ubuntu-based distributions: 

    # cp /etc/postfix/sasl/smtpd.conf /etc/postfix/sasl/smtpd.conf.bak

  3. Disable Digest-MD5 authentication for postfix by editing /usr/lib64/sasl2/smtpd.conf for CentOS or /etc/postfix/sasl/smtpd.conf for Debian/Ubuntu using a text editor and replacing the following line:

    CONFIG_TEXT: mech_list: DIGEST-MD5 CRAM-MD5 PLAIN LOGIN

    with

    CONFIG_TEXT: mech_list: CRAM-MD5 PLAIN LOGIN

  4. Restart the Postfix service to apply changes:

    # service postfix restart

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Comments

3 comments
Date Votes
  • Avatar
    Jon Doe

    We first noticed this problem like 10 years ago, and disabled DIGEST-MD5. Now I see that this value is still the default for new Plesk Obsidian 18.0.68 installations…

    According to https://datatracker.ietf.org/doc/html/rfc6331 DIGEST-MD5 has been marked as historic in 2011. I guess Plesk should start not using this anymore by default.

    1
  • Avatar
    Jon Doe

    With Plesk 18.0.72 now being able to hash passwords, you should also remove CRAM-MD5 from the list as this doesn't work with hashed passwords (server needs to know the plaintext password). Will lead to "SASL CRAM-MD5 authentication failed" errors.

    0
  • Avatar
    Dan McD

    What about auth_mechanisms = plain login scram-sha256? 

    0

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