"I love the fact that it's an intelligent mail application, not just a database tool. The fact that it reads and imports data from online forms is critical and it's implemented very nicely. There are also nice details throughout the program. It has very good filtering functions and comes equipped with many built-in filtering and import functions that anticipate common usage.
The customization capabilities, in general, are well done and vitally important. Also, details such as the fact that you can send out a test mailing to yourself before sending out a potentially flawed message to the entire list is really helpful.
The fact that it has a built-in mail server is fantastic. I haven't used it yet (so maybe it won't work they way I think it does), but the fact that it can handle huge amounts of mailings and it offloads the bandwidth to a dedicated server rather than setting off alarm bells at my ISP is really important and unique to this program.
I also have to applaud you on creating outstanding documentation. It's rare to have such simple yet informative documentation. Overall a superbly implemented, very useful program. Keep up the excellent work"