This blog explains the resolution for the NDR with error “‘550 5.7.106 APPROVAL.InvalidContent;”
4 Exchange 2016 in High Availability
2 Edge Exchange 2016
2 Hybrid Servers for the Mailbox Migration
1 On-premises Distribution Group
5 members where 4 mailboxes in Exchange Online and 1 mailbox in Exchange On-premises
Approver User mailbox is in Exchange Online
When an on-premises user is sending an email to this DL.
Approver receives the message and approves it.
But receives the following NDR.
Delivery has failed to these recipients or groups:
Microsoft Exchange (Guidemail@example.com)
Your message wasn’t delivered because the recipient’s email provider rejected it.
The following organization rejected your message: Exange201601.domain.com
Diagnostic information for administrators:
Generating server: Exange201602.domain.com
Remote Server returned ‘550 5.7.106 APPROVAL.InvalidContent; Invalid content. [Stage: OnCreatedEvent][Agent: Approval Processing Agent]’
Original message headers:
Important to observe the following:
- Mail flow is working fine between Exchange Online and On-premises.
- Edge Transport which is the 1st receive is not sending the NDR
- NDR is coming from Exchange 2016 mailbox role servers.
We ran the following command for all 4 Exchange 2016 Mailbox Role server which fixed this issue.
Get-ReceiveConnector “Default Servername” | Set-ReceiveConnector -TlsDomainCapabilities “mail.protection.outlook.com:AcceptCloudServicesMail”
This solution has been mentioned in the following forum post.
Hope this helps!
Prabhat Nigam (@PrabhatNigamXHG)
CTO @ Golden Five Consulting | CEO @ LAEXUG Foundation