Plesk notifications cannot be delivered to the recipient: 550-5.7.1 (or 550-5.7.26) This message does not have authentication information

Symptoms

• An email about bounce is sent by server to the administrator:

  Reporting-MTA: dns; example.com
  X-Postfix-Queue-ID: 53E6510D85C
  X-Postfix-Sender: rfc822; [email protected]
  Arrival-Date: Fri, 13 Oct 2017 03:45:16 -0500 (CDT)

  Final-Recipient: rfc822; [email protected]
  Action: failed
  Status: 5.7.1
  Remote-MTA: dns; ASPMX.L.GOOGLE.COM
  Diagnostic-Code: smtp; 550-5.7.1 This message does not have authentication
  information or fails to pass 550-5.7.1 authentication checks. To best
  protect our users from spam, the 550-5.7.1 message has been blocked. Please
  visit 550-5.7.1
  https://support.google.com/mail/answer/81126#authentication for more 550
  5.7.1 information. e99si513617itd.159 - gsmtp

• If the notification sent via Cron the next error can be found in the /var/log/maillog file:

  550-5.7.26 This message does not have authentication information or fails to 550-5.7.26 pass authentication checks. To best protect our users from spam, the 550-5.7.26 message has been blocked. Please visit 550-5.7.26 https://support.google.com/mail/answer/81126#authentication for more 550 5.7.26 information.

• Server does not have SPF and DKIM set-up

• Server does not have a valid rDNS

• Server's IP is blacklisted

Cause

Google requirements for mail servers is to have at least a valid rDNS and enabled SPF and DKIM to be able to deliver email messages.

Resolution

• Set correct rDNS for the server

• Remove server's IP address from blacklists:

  1. Navigate to spam list's server
  2. Follow the delisting procedure

• Enable SPF and DKIM:

  1. Navigate to Tools & Settings > Mail Server Settings;

  2. Enable SPF spam protection to check incoming mail to active;

  3. In case Plesk is the responsible nameserver for the domain enable DKIM spam protection;
  4. In case an external DNS server is used:
     • Retrieve DKIM records.
     • Add records manually on remote DNS servers.