phplist

phplist is a newsletter manager developed in PHP and MySQL that allows you to efficiently administer a database with more than 100,000 subscribers, all from its online interface.

It includes various interesting features, like the ability to keep track of which emails are opened, as well as the clicks that are recorded in each. You can then calculate statistics by message, subscriber, or URL.

phplist also supports sending attachments and creating RSS-based newsletters. Batch processing, message encryption, and throttling are just some of the other features of the application.

You can create your newsletters from phplist's interface using FCKeditor. The message format can be HTML or plain text. And, naturally, you can program when each is sent out.

Finally, phplist includes various templates that you can personalize to include subscription forms on your own webpage.