Mail delivery fails - Error 554: host refused to talk to me

Symptoms

• Mail delivery to particular domains fails with error in /var/log/maillog:

  PLESK_INFO: 0572C2801E1: uid=30 from=john.doe@example1.com
  0572C2801E1: message-id=6AD1BED0ECFB2E4FA52CC9B923AE4ED6A50F7157@example1.com
  0572C2801E1: from=john.doe@example1.com, size=3826, nrcpt=1 (queue active)
  0572C2801E1: host mx.example2.com refused to talk to me: 554 IP=IP_ADDRESS - A problem occurred. (Ask your postmaster for help or to contact info@mx.example2.com to clarify.) (BL)

• Checking mail connection using telnet:

  # telnet mx.example2.com 25
  Trying mx.example2.com....
  Connected to mx.example2.com.
  Escape character is '^]'.
  554 IP=IP_ADDRESS - A problem occurred. (Ask your postmaster for help or to contact info@mx.example2.com to clarify.) (BL)
  Connection closed by foreign host.

Cause

Error code 554 means IP-Blocking, remote mail server are not currently accepting e-mails from a server's IP address. This IP blocking may be due to a previously observed unusual volume of emails at the IP address concerned.

Resolution

Contact the remote mailserver administrator.

Additional info

What are spam protection general recommendations?