outbound spam filter policies

Question

Hi

I'm struggeling with Microsofts outbound spam filter policy in Exchenge 365. Automatic forwarding in my domain is set to "System Controlled". However, I would like to allow forwarding to certain external domains. The obvious thing would be to use remote domains.

This doesn't seem to work because of this: https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/external-email-forwarding?view=o365-worldwide

Remote domain settings and mail flow rules are independent of the settings in outbound spam filter policies. For example:

You allow automatic forwarding for a remote domain, but you block automatic forwarding in outbound spam filter policies. In this example, automatically forwarded messages are blocked  

OK, then to this...

You allow automatic forwarding in outbound spam filter policies, but you use mail flow rules or remote domain settings to block automatically forwarded email. In this example, the mail flow rules or remote domain settings will block automatically forwarded messages  

Unfortunaltely, I can't find a way in mail flow rules to allow forwarding to certain external domains and disallow everything else.

How can I do this? I believe I'm missing something obvious...

Thanks, Martin

Answer 1

Set the allowed forwarding to ON in the Outbound Policy:

Then create a mail flow rule to block autoforwards with the allowed domains as exceptions:

Reject with an explantion:

and stop processing rules:

Then for the domain exceptions. For the includes, enter the domain names ( contoso.com etc..)

But you aren't done!

You should also block PowerAutomate:

https://learn.microsoft.com/en-us/power-platform/admin/block-forwarded-email-from-power-automate

and Remove the ability to forward from OWA:

https://techcommunity.microsoft.com/t5/exchange-team-blog/the-many-ways-to-block-automatic-email-forwarding-in-exchange/ba-p/607579

Answer 2

Hi

Thanks for this. I've found another way in the meantime.

Set Forwarding On in Outbound Policy:
Allow Whitelist Domains in Remote Domain ("allow forwarding")
Disallow Forwarding in "Default Remote Domain"

Yours is nicer though as it allows a return message.

Martin