I was unable to reach a business this week who host their email on Office 365. Any email I sent would bounce with:

  550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)'

Something is rotten in the state of Outlook

outlook.com and Office 365 are very different beasts. with the latter problems are more often something (mis)configured by the customer/administrator of the 365 account rather than microsoft themselves, and there are steps the customer can take to work around the issue. With outlook.com there is nothing the recipient can do.