Update 04/13/2021 14:39 PM 14 days
Work is still ongoing with outbound-auth and outbound-xdgrid.
We were also made aware of bounces from M365 clients that use our smarthosts. The issue that caused that problem has been resolved, if your message bounced (if you received an error similar to below) please resend it.
Your message couldn't be delivered to the recipients shown below.
Sender not authorized for relay
Couldn't deliver the message to the following recipients:
How to Fix It
When Office 365 tried to send your message to the next server outside Office 365, that server reported an error that it couldn't relay your message. It's likely that the email server isn't correctly set up to receive and relay messages from your organization.
To fix this issue, forward this non-delivery report (NDR) to your email admin.
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More Info for Email Admins
Status code: 550 5.7.367
The sender's message was routed to an email server outside Office 365 that returned an error that it can't relay the message. It's likely that the server isn't set up correctly to receive and relay messages sent from yourdomain.com or from youruser.