YOU DO A GREAT JOB!
the Server is the best Mailserversolution i ever saw.
Also the manual is very good.
I used MS Exchange before and it was horrifying! Endless amount of Capacity, an old instable Jet-Database and easy to hack via IIS if you don´t spend a big amount of money to 3rd party products
Linux postfix is also not bad but you finish a keyboard until it´s well configured and if something goes wrong you need weeks of deep analyzing to get it fixed. (And it´s far away from being user-friendly)
Keep on the good work!