With the free service from MailChimp.com you are able to have 1,000 subscribers and 6,000 messages sent per month. Therefore if you have the limit of 1,000 subscribers, you can send 6 messages. But you will want to convert your account to a paid service once you reach this limit. More than likely, you will be earning enough commission from your list to pay for the monthly fees.
With MailChimp.com you can create Campaigns, Lists of users, and auto responders. They handle all the required unsubscribe and double-opt in requirements to run an email list and not break laws. Everything is customizable and there are a number of free Wordpress plugins that work with MailChimp.
Two plugins that I am currently using are MailChimp and AutoChimp. MailChimp is provided by the email service and will create a widget for you to show in your sidebar, allowing visitors to subscribe to your newsletter or list. AutoChimp was developed by Kyle Champman and integrates with the users of the site itself to automatically subscribe site users to your MailChimp list. A very nice feature also updates MailChimp with unsubscribes and user information, if you choose. AutoChimp has another feature that you might like, it can create campaigns from posts on your site. Therefore list subscribers will receive period updates in their email from you site posts.
One final plugin, not related to MailChimp, that might increase your site membership is Profiler. Profiler takes your site members and creates a page displaying them in groups of 10 or 20 (you choose). You can also have user photos and Gravatars. The user’s websites will be displayed within the membership listing. Therefore they receive a link back to their blog or website. This may entice some to join your site that would not normally.
Hope you utilize MailChimp’s free services and increase your online profits this holiday season.