An IP address of a Plesk mail server got blacklisted. How to troubleshoot?

Question

An IP address of a Plesk mail server got blacklisted. What to do?

Note: The following article covers cases when a local mail server is used by Plesk.

Answer

Table of Contents

• What are the symptoms if a Plesk IP address is blacklisted?
• Blacklist - what is it?
• Why an IP address got blacklisted?
• What to do if a server IP address is blacklisted?
• How to remove an IP address from blacklists?

What are the symptoms if a Plesk IP address is blacklisted?

• Mail cannot be sent to external mail addresses with a bounce message like:

  Note: In the output below, the IP address 203.0.113.2 belongs to a Plesk server.

  550 SC-001
  (SNT004-MC4F35) Unfortunately, messages from 203.0.113.2 weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).

  ---

  [203.0.113.2] The IP you're using to send mail is not authorized to 550-5.7.1 send email directly to our servers. Please use the SMTP relay at your 550-5.7.1 service provider instead. Learn more at 550 5.7.1 https://support.google.com/mail/?p=NotAuthorizedError h1si7104782plt.44 - gsmtp (in reply to end of DATA command))

  ---

  5.7.1 Service unavailable; client [203.0.113.2] blocked using
  prs.proofpoint.com (in reply to RCPT TO command)

  ---

  421 4.7.0 [TSS04] Messages from 203.0.113.2 temporarily deferred due to user complaints - 4.16.55.1; see https://help.yahoo.com/kb/postmaster/SLN3434.html

  ---

  550 mail not accepted from blacklisted IP address [203.0.113.2] (in reply to MAIL FROM command)

  ---

  MailEnable: Message could not be delivered to some recipients.
  The following recipient(s) could not be reached:
  Recipient: [SMTP:[email protected]]
  Reason: 554 Your access to this mail system has been rejected due to
  poor reputation of a domain used in message transfer

  ---

  The server returned:
  554 Blocked - see https://ipcheck.proofpoint.com/?ip=203.0.113.2

• When checking a server IP address using the MXToolbox blacklist checker or https://whatismyipaddress.com/blacklist-check, it shows that the IP address is in one of the DNS-based email blacklists (Commonly called Realtime blacklist, DNSBL or RBL).

• On Windows servers with MailEnable mail server, the following entries can be found in the SMTP-Activity logfile in %installation_path%Mail
EnableLoggingSMTP:

  Remote server returned a response indicating a permanent error. Server Response:(550 Mail content denied. http://mail.example.com/cgi-bin/help?subtype=1&&id=20022&&no=1000726**)

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  Communications Error: Socket connection to mta6.am0.yahoodns.net failed (error 10060). The host was eithe…