What exactly is an email marketing platform and what does it do?

What exactly is an email marketing platform and what does it do? An email marketing platform (EMP) is typically a 'Software as a Service' (SaaS) solution that marketers can use to manage their email subscribers and everything that goes with operating an email marketing channel effectively. (By the way, it's also commonly referred to as an email service provider, or ESP). There are lots of fancy and complex things that go on behind the scenes, but as users of such platforms, thankfully we...