This Autoresponder and Email Newsletter Plugin For WordPress plugin by Raj Sekharan adds a autopresponder to your blog with features like Aweber. You need to Subscribe to Expedition Post to download WP Responder.
Create Unlimited Number Of Newsletters – Apart from delivering blog posts to subscribers, you can create newsletters that are meant to be exclusively used for building a audience.
Create Unlimited Followup Autoresponders – Usually newsletter subscription plugins support only creating newsletters to which you must send broadcasts manually. With the WP Responder, you can create followup messages to get your prospects ready to buy your product or build a loyal following via E-Mail.
Create Post Series – For the longest time, creating a post series has been the way to increase blog subscribers. But most bloggers don’t promote their post series after they have finished up the series. This feature allows you to offer subscribing to a post series (posts filed under a certain category) by e-mail delivered at regular intervals such as once in 2 days.
Plugin homepage: http://www.wpresponder.com/