Exchange Online Sender receives this bounce-back: "Remote server returned '450 4.5.0 no recipient succeeded'
I can't find much information about this NDR.
I'm (Exchange 2013 on-prem) on the receiving end (sent from Exchange Online) of the issue. The error points to me, but I do not see the email in question passing through our edge firewall. The originating server and mailbox and many other
mailboxes can send mail to (as far as I can tell in the hub/frontend protocol/edge firewall, set verbose, logs and test messages) all my other mailboxes.
It only affects mail flow from one mailbox on Exchange Online to one mailbox on my
system and started around 1/12/19.
https://testconnectivity.microsoft.com
- Passed Inbound/Outbound SMTP for a variety of users.
- DNS tests passed.
Receiving mailbox in question.
- Get-MailboxRepairRequest passed.
- Not hitting quota.
I'm having the sending user try multiple clients (OWA/Outlook/Phone) to see if it is happening to one or all.