I run HubSpot’s Marketing Daily Newsletter, so I know quite a bit about email marketing and why an email marketing platform is one of the first additions to a marketer’s tool belt.

Email marketing is an effective way to engage and nurture leads into loyal customers. It’s also extremely cost-effective — some studies show an ROI of $40 for every $1 spent.

Leveraging email marketing can be difficult, especially if you’re trying to grow your list or manage the massive list you already have. Fortunately there are plenty of email marketing services available to help.

Here are 18 of the best ones I’ve found. I’ve even tested a few. Let’s dive in.