The error is coming from an M365 mail server, but you're talking about a user on GSuite.
Methinks someone had an account compromised, and Microsoft has "just said no".
Might be SPF / DKIM / DMARC issues too. But that error isn't from Google, you're looking at a ticket to Microsoft from your side to find out WTF is going on.
Try emailing it from something not Microsoft, see if it works.
So, I created another email account through Google workspace using a different username. So instead of the
jshmoe@customdomain.com I created a completely new account
joe@customdomain.com. Unfortunately, the results are the same. I can log into gmail.com using
joe@customdomain.com and successfully send an email, but when I try sending to
joe@customdomain.com I get the same error message:
The response from the remote server was:
550 5.4.1 Recipient address rejected: Access denied. [
BL6PEPF0001AB4C.namprd04.prod.outlook.com 2024-09-17T02:10:59.463Z 08DCD1D4F028DEEA]
However when I sent a test message from my old hotmail account I get a more verbose error:
BL02EPF00021F6B.mail.protection.outlook.com rejected your message to the following email addresses:
joe
@customdomain.com (joe@customdomain.com)
Your message was rejected by the recipient's domain because the recipient's email address isn't listed in the domain's directory. It might be misspelled or it might not exist. Try to fix the problem by doing one or more of the following:
- Send the message again - delete and retype the address before resending. If your email program automatically suggests an address to use, don't select it - type the complete email address.
- Clear the recipient Auto-Complete List in your email program by following the steps in this article. Then resend the message.
For Email Administrators
Directory based edge blocking is enabled for the recipient's organization and the recipient wasn't found in their directory. If the sender is using the correct address but continues to experience the problem, contact the recipient's email admin and tell them about the problem. To fix this they should resynchronize their on-premises and cloud directories.
I was hopeful this would be helpful, but a google search is telling me directory based edge blocking is an exchange feature. Which lines up with the block seeming to come from Microsoft (
BL02EPF00021F6B.mail.protection.outlook.com)
Since I have tried it with two different usernames it seems unlikely they were previously tied to a MS account. He is also a new employee so there is no reason to think that username@domain would ever have been used before anywhere.
Maybe the domain itself was previously hosted on exchange, but why would the owners email work fine?
Confused...