If you need a way to send out e-mails to a huge number of contacts then UniMailer helps you reach them.
UniMailer allows you to manage multiple groups of contacts but also makes e-mails to them feel more personal by allowing you to add a separate name to each one. UniMailer allows you to write plain text or HTML messages and supports attachments, although it doesn't seem possible to insert images into e-mails.
You can however track mail after it has been sent so that you get a delivery receipt on arrival. On the other hand, if you need to add lots of statistical data to e-mails, you can import it from Excel, which makes it a particularly useful tool for businesses. After sending, you've got a complete searchable archive of what you've sent, showing when and who to.
Most home users won't find much need for UniMail but small businesses will find it an invaluable tool.