Monday, August 28, 2017

O365 EOP Phishing Rule

I had a client last week that was constantly complaining about receiving a lot of phishing emails. I had done everything I could think of in order to try and mitigate them in Exchange Online Protection (EOP) and finally broke down and opened up a support case. Upon submitting the numerous examples to the support engineer he guided me through implementing an undocumented change to the phishing threshold via a header manipulation.

We created a mail flow rule that stated if the sender is outside of the organization and the recipient is the client's domain, then add a message header "MS-Exchange-Organization-PhishThresholdLevel" and set the value to 2 (the default is 4):



Ever since implementing this the client has said they are no longer receiving any phishing emails.

3 comments:

  1. Thank You! So, what exactly does setting that value to 2 do? How will this affect their legitimate external emails?
    Thanks

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    Replies
    1. Value of two increases the threshold of emails being flagged as phishing. It just runs the risk of legitimate emails being blocked/moved to the junk email folder.

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