We make it easy to send email newsletters to your customers, manage your subscriber lists, and track campaign performance. Unlike some of our competitors, we don't "dumb things down." We take extremely powerful tools that sophisticated marketers use (like segmentation, a/b testing, and ROI tracking), and we make them accessible to anyone.
Great personality, powerful mailer, easy to use, and reasonable pricing. You can't really ask for more from an email marketing service, unless you are a designer who wants to control every last detail of the email's look.
I have just begun using Mailchimp and I echo everyone's sentiment that it works exactly as advertised at an attractive price point. If I could just have a little more flexibility on design, then I would tack on that extra star.
A fantastic resource! Incredible set of options, great customer service and the fact that it's FREE to start is a huge win. My favorite feature? The RSS-to-Email functionality. It allows you to auto-draw your blog and other RSS items (jobs, events, listings, etc.) directly into the e-mail and send automatically. If you're a startup, thinking about e-mail, MailChimp is the answer :)