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

Created:

2016-11-16 12:39:29 UTC

Modified:

2017-04-24 11:02:44 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

  • When 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` return ` smtpd_use_tls = yes`
[root@server]# postconf smtpd_use_tls
smtpd_use_tls = yes

Cause

Postfix is configured to allow SMTP authentication over TLS secured 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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