It seems like all the major Marketing Automation clients have this feture. It's important to see what your email will look like in all the browsers / Email Clients / Screens
This would be a great future to add to the Marketo powerhouse.
If you have this as part of your instance, you should see a Deliverability Tools tile when you are in My Marketo. If you do not see this, it's likely not part of your subscription or check with your account rep.