alt Hacker Newsyes ... i thought this is included in the expression "as a service" :)
it doesn't matter how you slice & dice it, the "service" is to have someone - be it business or be it a person - who is responsible for running this service ... you get an SLA and according to the conditions you are able to work with the entity which provides the service ...
If the person you pay is an employee you do not get the external guarantee, nor would you if you pay someone to maintain a server that is yours.
The big email providers do not really provide a worthwhile SLA to most customers AFAIK. Do they cover the cost of business interruption if your business is heavily dependent on email, for example?