Thanks Paul.
Yep, I knew it had nothing to do with O365, it's just that QB were adamant it did route through it somehow and I had to contact Microsoft. They just would not accept it was their email servers and instead falsely claimed it routed through my email servers. I just find it ludicrous but at the same time extremely scary that they gave me an impossible task of contacting Microsoft and asking them to look into an issue which had absolutely nothing to do with them.
