I've worked for a real estate webhost and a major cloud provider/isp. Both had nightmarish problems simply ensuring email delivery. It did not help that the rea

I've worked for a real estate webhost and a major cloud provider/isp. Both had nightmarish problems simply ensuring email delivery. It did not help that the real estate "bulk mail newsletters" were legitimate spam. At the ISP, we offered an open internal relay to customers for some reason, and thus were again legitimate spammers. MS has 2 layers of spam blocking - one for Outlook.com, and a much stricter invisible layer for O365 with no support team.