Comment by rwmj

As another data point: MSFT have some sort of open mail server/service called onmicrosoft.com which (in my experience anyway) is only being used to send out fraudulent paypal messages. Because it lets the spammer set the From to [email protected] and also contains valid DKIM etc, it sails past spam filtering. There are so many complaints about this on (real) paypal.com forums, but Microsoft are apparently unable to do anything about it.