I have started to see frequently email deliverability issues with mail going through my Cloudflare proxied service. I do not have this issue with mail going through my hosting provider (Hostgator). I do have DKIM , SPF and DMARC configures correctly on both ends. Here is an example of one error (with email addresses removed). I’ve been receiving these error with multiple receivers not just one domain. It happens with multiple domains to different people.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
host eig-east.smtp.a.cloudfilter.net [3.228.35.199]
SMTP error from remote mail server after end of data:
550 Seahqn3sG2t4aSeahqQyOJ - <emailaddress > message rejected AUP#SNDR
Reporting-MTA: dns; gator4079.hostgator.com
Action: failed
Final-Recipient: rfc822;emailaddress
Status: 5.0.0
Remote-MTA: dns; eig-east.smtp.a.cloudfilter.net
Diagnostic-Code: smtp; 550 Seahqn3sG2t4aSeahqQyOJ - <sender> message rejected AUP#SNDR
Return-path: <sender>
Received: from [99.36.0.71] (port=56511 helo=smtpclient.apple)
by gator4079.hostgator.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
(Exim 4.96)
(envelope-from <sender>)
id 1qSeaf-0007MW-1P
for ;
Sun, 06 Aug 2023 09:18:43 -0500