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SOLVED: Remote Server returned '420 4.2.0 Recipient deferred because there is no Mdb'
How to fix Non-delivery report error '420 4.2.0 Recipient deferred because there is no Mdb' by running Enable-RemoteMailbox PowerShell
Problem: Non-delivery report (NDR) error '4.2.0 Recipient deferred because there is no Mdb'
Non-delivery report error when trying to send emails to a user in an Office 365 - Exchange Hybrid environment
Delivery has failed to these recipients or groups:
Delivery has failed to these recipients or groups:
Remote Server returned '420 4.2.0 Recipient deferred because there is no Mdb'
Solution: Run the Enable-RemoteMailbox PowerShell command
This error is caused by the user not existing on the Exchange hybrid server. The mailbox is missing the user@domain.mail.onmicrosoft.com smtp address, which is used as the remote routing address to send emails to Office 365
To fix this, run the following PowerShell from the Exchange Hybrid server.
Enable-RemoteMailbox user@domain.com -RemoteRoutingAddress user@domain.mail.onmicrosoft.com
See this guide for more information about this problem
SOLVED: Office 365 - AD Synced user not showing in Exchange Hybrid on-premises
https://techlabs.blog/categories/office-365/solved-office-365-ad-synced-user-not-showing-in-exchange-hybrid-on-premises
SOLVED: Office 365 - AD Synced user not showing in Exchange Hybrid on-premises
https://techlabs.blog/categories/office-365/solved-office-365-ad-synced-user-not-showing-in-exchange-hybrid-on-premises
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