As mentioned you will need an smtp relay, and yes MSL is perfect (as is IIS on a windows box).
You will need an SPF record created for the domain that includes the public IP that the mail will be appearing from, and you will need to then relay it to O365 from your internal relay. If you don't have the SPF record the mail will be dropped at O365 as it will be detected as spam.
Then just point MCD/MiVB at the smtp relay and you should see mail starting to flow.