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Unable to send an email from a Plesk server with Postfix: SASL login authentication failed

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Kuzma Ivanov
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Plesk for Linux kb: technical ABT: Group B

Applicable to:

  • Plesk for Linux

Symptoms

  • When sending an email from webmail, the following error message is shown:

    PLESK_INFO: SMTP Error (535): Authentication failed.

  • The following error message appears in /var/log/maillog:

    CONFIG_TEXT: postfix/smtpd[7538]: warning: unknown[203.0.113.2]: SASL login authentication failed: authentication failure

  • The saslauthd service is up and running on the server:

    # service saslauthd status
    ...
    Active: active (running) since ...

Cause

The Postfix smtpd.conf configuration file is corrupted.

Resolution

  1. Connect to the Plesk server via SSH.

  2. Open the smtpd.conf file in a text editor (in this example, we are using the vi editor) and edit the file as follows:

    • on CentOS/RHEL-based distributions

      # vi /usr/lib64/sasl2/smtpd.conf

      pwcheck_method: auxprop saslauthd
      auxprop_plugin: plesk
      saslauthd_path: /var/spool/postfix/private/plesk_saslauthd
      mech_list: DIGEST-MD5 CRAM-MD5 PLAIN LOGIN
      sql_engine: intentionally disabled
      log_level: 4

    • on Debian/Ubuntu-based distributions

      # cat /etc/postfix/sasl/smtpd.conf

      pwcheck_method: auxprop saslauthd
      auxprop_plugin: plesk
      saslauthd_path: /private/plesk_saslauthd
      mech_list: DIGEST-MD5 CRAM-MD5 PLAIN LOGIN
      sql_engine: intentionally disabled
      log_level: 4

  3. Save the changes and close the file.

  4. Restart the saslauthd service:

    # service saslauthd start

Comments

7 comments

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  • Avatar
    Miomir Besarabic

    On Ubuntu is /etc/postfix/sasl and not /usr/lib64/sasl2. Please correct your article.

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    Ivan Postnikov

    Hello @Miomir, the article will be updated soon.

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  • Avatar
    R Broersma

    On Debian 10 there is no saslauthd (and never has been)

    # service saslauthd status
    Unit saslauthd.service could not be found.

    Yes, Postfix is complaining about unreachable saslauth...

    Apparantly, saslauthd is/should be ran bij Postfix, as it is listed in master.conf.

     

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  • Avatar
    R Broersma

    The documentation in this article is wrong. A recent Plesk update breaks Plesk saslauthd on Postfix which changed the chroot flags of a lot of services in /etc/postfix/master.cf.

    The solution mentioned for CentOS (setting saslauthd path to the full system path, instead of the chroot) works for Debian machines as well.

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  • Avatar
    Gjimi

    # service saslauthd start
    Failed to start saslauthd.service: Unit saslauthd.service not found.

    Debian 9

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    Ivo Smits

    1. The service saslauthd start command is incorrect, most debian/ubuntu systems use systemctl instead of the service command

    2. the config "saslauthd_path: /private/plesk_saslauthd" as listed for debian/ubuntu seems incorrect, the value for CentOS/RHEL "saslauthd_path: /var/spool/postfix/private/plesk_saslauthd" worked on my Debian system.

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  • Avatar
    Kuzma Ivanov

    Hi there Ivo Smits,

    Thanks for your input!

    1. The "service" command still works on all Debian/Ubuntu systems. It does not matter which command you use, "service" or "systemctl", to start a service.

    2. In the config line "saslauthd_path: /private/plesk_saslauthd", "/private/plesk_saslauthd" is a default chrooted path. If it works for you with "/var/spool/postfix/private/plesk_saslauthd", then most likely you have hit a bug in Plesk Obsidian 18.0.34 described here.

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