SMTPS connection from Outlook to Plesk for Linux server does not work: SASL authentication failure: realm changed: authentication aborted

Symptoms

• On a Plesk for Linux server, Postfix is used as a mail server.
• SMTPS connection from Outlook to the Plesk server fails to be established.
• The following errors are found in the file /var/log/maillog:

  SSL_accept error from unknown[203.0.113.2]: lost connection
   lost connection after CONNECT from unknown[203.0.113.2]
  plesk postfix/smtpd[6814]: warning: SASL authentication failure: realm changed: authentication aborted
  plesk postfix/smtpd[6814]: warning: 203.0.113.2.example.com[203.0.113.2]: SASL DIGEST-MD5 authentication failed: authentication failure

• Plaintext authorization is disabled in Postfix:

  # cat /etc/postfix/main.cf | grep “smtpd_sasl_security_options”
  smtpd_sasl_security_options = noplaintext

Cause

Outlook is not compatible with CRAM-MD5 authentication mechanism.

Resolution

1. Connect to the server using SSH.
2. Open the file /etc/postfix/main.cf for editing.
3. Comment out the following line by putting “#” at its beginning and save the changes:

   #smtpd_sasl_security_options = noplaintext

4. Restart postfix to apply configuration changes:

   # service postfix restart