Mike, if you check out the archives, you will see that this issue is
bandied about on NT-ISP every two weeks or so. There is no clear consenus,
and it is doubtful that there will ever be. If one product was the best,
and met everyone's needs, then there would be only one product on the
market, n'est-ce pas?
What is best for you will depend on the exact features; more importantly,
will it work for you? Once you find it, grab it!
For what it's worth, I'm an IMail fan. It was the first email package I
started with, and I like the fact that clients can use a web
interface...but I will admit that EACH packages has strengths, and
Cry Havoc, and let slip the dogs of war...