Block BCC messages sent to distribution groups

By default inbox-processing rules don’t process the BCC line, for privacy reasons. This means that if you have a carefully-crafted rule in your mailbox to divert Distribution Group messages to a subfolder, the rule won’t work if someone’s doing a reply-all via a BCC.

However Microsoft’s Exchange Team have now come up with a new powershell cmdlet which can resolve this behaviour. They’ve introduced a new ‘blockbcc’ switch to the set-distributiongroup cmdlet. Once set this will ensure that anyone trying to reply to a group via BCC will get a non-delivery report saying that they’re not allowed to do that.

It has user-friendly text:

The group [distribution group name] doesn’t accept messages sent to it as a BCC recipient.
How to fix it:
The message wasn’t delivered to the group because it doesn’t support sending to it as a BCC recipient. To fix this, try one of the following:
-Remove the group from the BCC adress box and add it to the To or the Cc box instead.
-Ask the owner of the group to change the setting to allow sending messages to it as a BCC recipient.
This bounce message only applies to the group or groups mentioned here. Unless you’ve gotten other bounce messages for other recipients, anyone else you sent the message to should have received the message’.


From a Nexus-team perspective, we need to do the following PowerShell to make this happen:

Set-DistributionGroup -Identity [group's name] -BlockBCC $true

Or to check:

Get-DistributionGroup -identity [group's name] | fl BccBlocked
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