Phish threat emails being deleted by Outlook

Hello, Apologies if this is in the wrong forum. Outlook seems to be automatically deleting emails from Phish threat.

I've whitelisted the domains/IP's in Office 365, added the TXT records to our domain, added the proper whitelists in the mail flow rules in MS 365.

Emails are still getting quarantined by Microsoft. 

After releasing them from Quarantine, they're landing in people's inboxes, staying there for about 5 seconds, and then being automatically wiped off the face of the earth by Outlook somehow (multiple users, even with no rules in place).  This has been happening repeatedly for two months.  Test messages come through without issue, but once I send out the actual campaign they're immediately flagged and deleted. 

What am I missing and where do I start?