According to reviews Earth Class Mail is among the worst of these services (though they have better web design and better PR). PaperlessMail.com and sbimailservice.com are better reviewed, and the prices end up being a lot lower. I don't have enough experience to say what is best, or whether Earth Class Mail deserves its bad reputation, but I did spend a lot of time reading up on it, since it's pretty important that mail works right for me to be able to keep running Virtualmin.