Understand if email error is due to sender or recipient server

Question

When I try to send emails to a well-known customer of mine, I receive this error:

Reporting-MTA: dns; googlemail.com
Received-From-MTA: dns; <my email>
Arrival-Date: Sat, 11 Jan 2020 03:55:20 -0800 (PST)
X-Original-Message-ID: <msg-id>

Final-Recipient: rfc822; <customer's email>
Action: failed
Status: 5.0.0
Remote-MTA: dns; <domain>.com. (<customer's server address>, the server for the domain <domain>.com.)
Diagnostic-Code: smtp; 571 Delivery not authorized, message refused
Last-Attempt-Date: Sat, 11 Jan 2020 03:55:22 -0800 (PST)

Trying with another smtp server:

Reporting-MTA: dns; smtpcmd09.ad.aruba.it [62.149.128.218]
Received-From-MTA: dns; [192.168.1.104] [<my ip>]
Arrival-Date: Sat, 11 Jan 2020 12:44:11 +0100

Final-recipient: rfc822; <customer's email>
Action: failed
Status: 5.1.1
Diagnostic-Code: smtp;  571 Delivery not authorized, message refused
Last-attempt-Date: Sat, 11 Jan 2020 12:44:11 +0100

My provider says:

The error is raised by the remote server (customer) because there's the Final-Repicient field

Instead, the IT service of my customer's company says:

The messages talk about smtp so it's up to your provider to understand and fix why those emails are not sent to us

Other details:

• I can send emails to any other domains, but this one
• I can receive emails from all domains (including this one)
• they say have no problems at all, but me

Any chance to have a clarification about the messages above? Personally, I think Final-Recipient is just the destination email and it has nothing to do about the error itself.

Bottom line: Delivery not authorized - by whom?

Solution

The receiving server blocks you. This can have multiple reasons, like:

• Your ip or ip-range is being blocked because it's on some abuse list (consumer ip addresses usually are)
• Reverse lookup on your ip doesn't work
• your ip is on a blacklist.
• even more reason

But no doubt, the receiving server blocks you. It's just a matter of finding out why.

Has been asked before here: Mail Delivery Failure - Reason: 571 Delivery not authorized, message refused

And there's some extensive explanation here: https://bobcares.com/blog/how-to-fix-571-delivery-not-authorized-message-refused/