The "Install and Security Howto" describes how to setup a secure eGroupWare server include mail server, firewall and other services. The book and the example scripts for this book will help you to setup a secure environment.
Seems to be a very good groupware suite. Since I won't touch mono with a ten-foot pole, this is a good solution. It still needs a bit of fixing of a couple of minor problems, but over all this is a good effort.