Simple SMTP integration for existing mailing- we change the SMTP servers to point to Message Bus, which is a simple change for us to make on our servers and then deploy. A minute later we can be sending mail via Message Bus. One feature they have which I really like is the way they separate your email into different channels. It's really simple for us to do. You essential just put code in the from address (an ID) which they then strip out later. One of our engineers set it up in less than an hour. We had it all configured and we were getting analytics- more than we ever had for each email, relatively quickly without a whole lot of integration necessary. They provide us with metrics for opens and clicks. This is especially helpful because we didn't have analytics for transactional emails before hand with the previous solutions we used. We were sending them straight thru to simple email services such as AWS (we've used a number of email providers). AWS's SMTP option doesn't do any link wrapping. Message Bus has really simple analytics and it's an easy integration. The API has excellent and clean documentation. Upfront there were very few questions about how to do something because of the great documentation they provide. This is especially important because some other solutions have undocumented API's.