An email about bounce is sent by server to the administrator:
Reporting-MTA: dns; example.com
X-Postfix-Sender: rfc822; [email protected]
Arrival-Date: Fri, 13 Oct 2017 03:45:16 -0500 (CDT)
Final-Recipient: rfc822; [email protected]
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
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
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
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.
Remove server's IP address from blacklists:
- Navigate to spam list's server
- Follow the delisting procedure
Enable SPF and DKIM:
Navigate to Tools & Settings > Mail Server Settings;
Enable SPF spam protection to check incoming mail to active;
- In case Plesk is the responsible nameserver for the domain enable DKIM spam protection;
- In case an external DNS server is used:
- Retrieve DKIM records.
- Add records manually on remote DNS servers.