Sending outreach proofing emails is not being trusted by Outlook. Why?

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I'm trying to prepare for sending out our first outreach email blast to our customers.  However, when I try to send the proof version of the email from the tool to our internal team, Outlook is blocking it from ever being received.  Is there some setting that needs to be applied to allow the emails sent from the outreach mailbox to be considered as a trusted source?  

I get an error message from this too when trying to test sending the proof to my personal hotmail account.  At least it comes through there, though.  But that error message indicates that "This sender failed our fraud detection checks and may not be who they appear to be."