Ironmail (Score 1)

It's used by many of the largest and most succesful companies across the world. With good reason - it works!

Now keep in mind this is a gateway solution: It screens incoming and outgoing mail for spam and viruses plus a whole lot more.

You still need a solution for storing the mail for 1 million accounts, but Ironmail will interface with any of them.

www.ciphertrust.com