EOP and 3rd party email filtering

Question

I have a case where one Org is using a 3rd party email filtering service. (MX records point here) They have whitelisted several email domain / email address on that service

Some of the messages are going into the user junk folders in outlook . (just started recently in October apparently)

Customer wants to either disable EOP altogether (spam policy) or if that's not possible and they must use double filtering . what needs to be done in EOP?

Will they have to create duplicate filtering rules / whitelist in EOP now as well?

What is the recommended approach here?

Answer 1

You would need to create a transport rule that sets the SCL to -1 for messages coming the 3rd party IP addresses.

Alternatively, use enhanced filtering to take advantage of EOP filtering as well and then create rules that allow messages based on the original IPs of the senders

https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/enhanced-filtering-for-connectors

Answer 2

Hi @dirkdigs

Yes, I agree with the suggestions above from Andy, the official document introduces the scenario MX record points to third-party spam filtering , you could refer to this link to get more information.

And instead of bypassing spam filtering using a mail flow rule, we highly recommend that you enable Enhanced Filtering for Connector (also known as Skip Listing). Most third-party cloud anti-spam providers share IP addresses among many customers. Bypassing scanning on these IPs might allow spoofed and phishing messages from these IP addresses.

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