SMTP authentication fails with SMTP Error (250): Authentication failed

Created:

2016-11-16 12:39:29 UTC

Modified:

2017-06-21 19:43:22 UTC

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SMTP authentication fails with SMTP Error (250): Authentication failed

Applicable to:

  • Plesk 12.5 for Linux
  • Plesk Onyx for Linux
  • Plesk 11.0 for Linux
  • Plesk 11.5 for Linux
  • Plesk 12.0 for Linux

Symptoms

  • Trying to send email using Roundcube an error occurs:
    SMTP Error (250): Authentication failed
  • When connecting via telnet, the following output is displayed:
    # telnet mail.example.com 25
    Trying 203.0.113.2...
    Connected to mail.example.com.
    Escape character is '^]'.
    220 mail.example.com ESMTP Postfix
    HELO l
    250 mail.example.com
    AUTH LOGIN
    503 5.5.1 Error: authentication not enabled
  • Mail server does not return authentication mechanisms list:
    # telnet 203.0.113.2 25
    Trying 203.0.113.2...
    Connected to 203.0.113.2
    Escape character is '^]'.
    220 mail.example.tld ESMTP Postfix
    EHLO example.com
    250-mail.example.com
    250-PIPELINING
    250-SIZE 20480000
    250-ETRN
    250-STARTTLS
    250-ENHANCEDSTATUSCODES
    250-8BITMIME
    250 DSN

  • The command postconf smtpd_use_tls returns smtpd_use_tls = yes
    # postconf smtpd_use_tls
    smtpd_use_tls = yes

Cause

Postfix is configured to allow SMTP authentication over TLS secure connection, but TLS authentication is not correctly configured.

Resolution

Execute the following to maintain SMTP authentication compatibility with non-TLS clients:

# postconf -e smtpd_tls_security_level=may
# postconf -e smtpd_use_tls=no
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