Mail gets rejected: Client host blocked using zen.dnsbl


2016-11-16 13:01:15 UTC


2017-07-09 14:56:09 UTC


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Mail gets rejected: Client host blocked using zen.dnsbl

Applicable to:

  • Plesk 11.0 for Linux
  • Plesk 11.5 for Linux
  • Plesk 12.0 for Windows
  • Plesk 12.0 for Linux


Inbound email from specific servers gets rejected/blocked. In mail client following message appears:

An error occurred sending mail: Unable to establish a secure link with SMTP server using STARTTLS since it doesn't advertise that feature. Switch off STARTTLS for that server or contact your service provider.

In /usr/local/psa/var/log/maillog file there are following messages:

localhost postfix/smtpd[17588]: NOQUEUE: reject: RCPT from mail.server: 554 5.7.1 Service unavailable; Client host [] blocked using zen.dnsbl;; from=<mail@domain2.tld> to=<mail@domain1.tld> proto=ESMTP helo=<mail.server>
localhost /usr/lib64/plesk-9.0/psa-pc-remote[21418]: Message aborted.


The IP-address of sending server is listed in spam black lists.


Either delete blocking spam list server from Plesk in Tools & Settings > Mail Server Settings > Switch on spam protection based on DNS blackhole lists > DNS zones for DNSBL service or check more information in the URL provided at maillog

The spam blacklist tool may also be defined in /etc/postfix/ , for example:

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