Cannot receive emails: Client host rejected: Service unavailable

Symptoms

• Cannot receive emails. The following error may be found in /var/log/maillog :

  CONFIG_TEXT: postfix/smtpd[5105]: NOQUEUE: reject: RCPT from unknown[203.0.113.2]: 450 4.7.1 <203.0.113.2>: Client host rejected: Service unavailable; from=<john.doe@example.com> to=<john.doe@example.org> proto=ESMTP helo=<[203.0.113.2]>

• Warnings in /var/log/maillog :

  CONFIG_TEXT: postfix/smtpd[5105]: warning: 192.0.2.2.dnsbl.example.net: RBL lookup error: Host or domain name not found. Name service error for name=192.0.2.2.dnsbl.example.net type=A: Host not found, try again

• The Postfix configuration parameter smtpd_recipient_restrictions is configured to use DNSBL service dnsbl.example.net in /etc/postfix/main.cf file:

  # grep dnsbl.example.net /etc/postfix/main.cf smtpd_recipient_restrictions = ...permit_dnsbl_client dnsbl.example.net=192.0.2.2,

Cause

Plesk is configured to use non-existent DNSBL service.

Resolution

1. Log in to Plesk.

2. Remove the non-existent DNSBL in Tools & Settings > Mail Settings:

   

Also, it can be done using command line:

1. Log in to Plesk using SSH.

2. Remove non-existent DNSBL service dnsbl.example.net from Postfix configuration file /etc/postfix/main.cf:

   CONFIG_TEXT: # permit_dnsbl_client list.dnsbl.example.net=192.0.2.2

3. Restart Postfix:

   # service postfix restart