Recipients are not found via Recipient Filtering

Question

Hey,
i have the following issue with a customer:
The customer get an email from an external sender like:
sender: [email protected]
recipients: [email protected];[email protected];[email protected] etc.
In the example the accounts 1 and 2 exist and 3 is a non existing address.
We have enabled Recipient Filtering / Recipient Vaildation and the example mail above get defered because of the non existing address [email protected] the recipients 1 and 2 did also not receive this email.
How can we change this behaviour? 1 and 2 should get this mail and for 3 there should be an 550 user unknown or in this case an ndr, since the mail object contains other valid recipients.
Also, i've noticed that some mails get discarded with "user unknown", although the recipient exists. How can that be?

Answer 1

Hi Peter,
Based on my research, I found something useful for your reference:
When recipient filtering on a Mailbox server detects one invalid or blocked recipient in a message that contains other valid recipients, the message is rejected.
More details in the following article:
Manage Recipient Filtering on Edge Transport Servers
http://technet.microsoft.com/en-us/library/bb125187(v=exchg.150).aspx
Maybe the user 3 is the problem, please delete it from the recipient list for testing.
About no NDR returns, I suggest double check whether the NDR is enabled. If not, please enable it via following command:
Get-RemoteDomain | Set-RemoteDomain -NDREnabled $True
Hope it is helpful
Thanks
Mavis
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