O365 / EOP / "This Sender Failed Our Fraud Detection Checks"

[CapnPugwash]

We have O365 in a hybrid config with on-pre Exchange 2010. This has been up and running for over a year with no issues.

 

We have a number of photocopiers with 'scan-to-me' , a user scans a document & it is emailed to themselves.

 

Today I have had two users complain that the emails are being pushed into there junk mail folders, the emails contain the legitimate O365/EOP message "This Sender Failed Our Fraud Detection Checks and May Not Be Who They Appear to Be"

 

I've just done a scan-to-me test and it worked fine. This doesn't appear to be affecting all users & there is nothing unusual about the users that it is affecting, previously they could use scan-to-me with no problems.

 

I've seen articles suggesting that this is an SPF issue... which I doubt because if it was , wouldn't that affect everyone?

 

If anyone has any ideas, please let me know!