ESP or EMS

The correct answer is that we're both, plus much more!

Those terms are generally used to refer to platforms that strictly focus on email. In Marketo, email is just one of many channels customers use to build relationships with customers. For that reason, most people wouldn't use those terms to describe Marketo. Industry folks previously described Marketo as a "marketing automation (MA)" platform. But because we've grown to do much more than lead management, Gartner/Forrester (and others) now refer to Marketo more broadly as an "enterprise marketing suite" or "digital marketing platform"