Outlook fails to send an email. SASL authentication failure

  • Created:

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:

    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:

    mech_list: DIGEST-MD5 CRAM-MD5 PLAIN LOGIN

    with

    mech_list: CRAM-MD5 PLAIN LOGIN

  4. Restart the Postfix service to apply changes:

    # service postfix restart