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WP-AJAX Newsletter
Housed at Google code, apparently this plugin allows for a newsletter to be emailed to all registrants of blog content. Lots of ability to customize the outgoing newsletter, as well as an AJAX powered registration (including email conformation for registration). I couldn’t decipher if you could include content outside of blog posts or not.
Instinct Entertainment
According to the authors “WP Campaign Monitor is an email newsletter / SMS tool built for WP users who want to send campaigns, track the results and manage their subscribers. Version Two will integrate with e-commerce lite.” I haven’t tested this, but there very well is a demand for such plugins, especially for those developing WP more as a CMS. While there, checkout the e-commerce plugin. A lot of development has been done since its first introduction.
BlogMailr - Publish from your email straight to your blog
Not WP specific, but for those that want an easy to use method of blogging by email, this free service seems like an easy option. Not tested yet, but I did see a demo on another WP blog. Their site says it supports both file uploads and tagging. Especially handy I’m sure for those that want to post from mobile devices.
Skippy has stopped development of his Subscribe2 plugin, and passed the torch to Matt at Prescribing Advice. Matt is actively developing the plugin, with a recent release that added user option to define Reminder Email, improved array handling, improves Web Standards Compliance in the Subscribe2 pages.
For those not familiar with Subscribe2, it basically allows those not yet tech savy enough to use RSS to subscribe to your blog via email.
Vicent Prat
This plugin could be useful for sites that utilize the roles feature of WordPress. It allows for emails to be sent to registered users based on their role. So if you just want to contact the contributers, for instance, this makes it easy to do directly from your admin panel. It simply adds as new submenu to your write panel.