We just started using MailChimp because it seems to be the only one that offers a free account for small or new users. The problem is that there are so many steps for a potential subscriber to go through with both double opt-in and recaptcha, that we are getting at best complaints to worst, plain nasty comments posted on our Facebook page. We don’t know how many would be subscribers we lost because of this.
List fatigue is also a concern. If you're buying a list from a trade show, keep in mind that the other vendors at the trade show, and even businesses elsewhere who bought the list, are also emailing these recipients. By the time you reach the recipients’ inboxes, those readers are going to be exhausted by the barrage of unsolicited commercial email they've been receiving.
Julie Ewald recommends moving away from sending generic content to your whole email list via e-blast entirely. With a little elbow grease, you can utilize segmentation and start sending off tailored messages to each of your lists with content that’s relevant, valuable, and designed to resonate with the kind of recipients that make up each segment.