Mail gets rejected: Client host blocked using zen.dnsbl

Refers to:

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

Created:

2016-11-16 13:01:15 UTC

Modified:

2017-01-27 23:32:03 UTC

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Mail gets rejected: Client host blocked using zen.dnsbl

Symptoms

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 mail.solarnex.com 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 [1.2.3.4] blocked using zen.dnsbl; http://www.spamhaus.org/query/bl?ip=1.2.3.4; 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.

Cause

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

Resolution

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/main.cf, for example:

reject_rbl_client new.spam.dnsbl.sorbs.net
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