I'm sorry to have to inform you that your message could not be delivered

We are getting this message quite a bit:

This is the mail system at host box.fwla.com.

I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own text from the attached returned message.

               The mail system

______@toshiba.com: host
toshiba-com.mail.protection.outlook.com[] said: 550 5.4.1
[______@toshiba.com]: Recipient address rejected: Access denied
(in reply to RCPT TO command)

I do get a perfect 8.7/10 on mail-tester.com.
-0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid
This negative score will become positive if the signature is validated. See immediately below.
0.1 DKIM_VALID Message has at least one valid DKIM or DK signature
Great! Your signature is valid
0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author’s domain
Great! Your signature is valid and it’s coming from your domain name
-0.001 HTML_MESSAGE HTML included in message
No worry, that’s expected if you send HTML emails
-0.001 MIME_HTML_MOSTLY Multipart message mostly text/html MIME
-1.985 PYZOR_CHECK Listed in Pyzor (http://pyzor.sf.net/)
0.55 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain
0.001 SPF_HELO_PASS SPF: HELO matches SPF record
0.001 SPF_PASS SPF: sender matches SPF record
Great! Your SPF is valid

The PYZPR CHECK is new. It hasn’t come up before today.

I do not send SPAM.

Well that’s concerning. Is Pyzor rejecting your other messages too?

Do they all have the same content?

Oh wait, I thought that was some headers from a message you sent. That’s actually what mail-tester.com said? If so, then that Pyzor error depends on what garbage you type into the message you send to mail-tester. It’s silly of them to include it. Ultimately, mail-tester is too simple to be very useful. A high score just means you’re running mail-in-a-box. : )

You’re going to have to look at the headers from the actual emails that got rejected for hints.

Also, it couldn’t hurt to see if your IP is on any blacklists. See MXToolbox and the Systems Checks in https://mailinabox.email/guide.html

Thanks. That’s a good start. I used mxtoolbox right when I fire up new servers to check the IP address assigned. They are clean but I will inspect message headers and report back.