There are literally so many options online when it comes to finding an E-Mail marketing tool. Before even stopping to search for relevant tools, you have to first ask yourself a few pertinent questions, including what you even need your autoresponder/e-mail marketing tool for? Answering this question will ensure that you have a far better idea of the type of features you really need and you can discount those that you do not. Taking a broad stance, most people are looking for e-mail marketing software because they want to manage their own e-mail list, send relevant e-mails to their subscribers and ensure a high rate of deliverability. The over-arching aim for any mailing list is to generate profit.
The first thing you should be concerned about when scoping for e-mail marketing software is the deliverability rate of the tool in question. Why is this important? Well first off, so many tools out there cannot guarantee that the e-mails you send out via the tool will actually be delivered to the location you have specified i.e. your subscriber's inboxes. If your mail isn't delivered then you can't profit from your list. There are a number of things that can affect the deliverability rate of your e-mails including whether or not the e-mails you are sending out have been blacklisted by various ISPs. Always look for a reputable tool that can give you some sort of guarantee that your e-mails will reach your subscriber's. Always keep in mind that the deliverability rate is also dependent on the content of the e-mails, so be cautious when it comes to buying into marketing gimmicks like "95% deliverability rate".
A second thing you should always be on the lookout for is autoresponder functionality. You want to be able to customise the e-mails you send out and you want to be able to schedule them in for delivery and segment your subscribers into various groups so that when they sign-up they can receive a particular e-mail you have scheduled for delivery.