I'm currently researching the best solution for a large email service. The solution must be unix/linux based. It must have clustering and mirroring. It must scale to basically unlimited users. It must have a good management system to add new servers for expansion, and also a good system to manage the users.
So far, it seems to me the best solution for what I'm looking for is: http://www.axigen.com/
I have also looked at:
Is there an open source product that has clustering and mirroring? Is there any other products I'm missing? Anybody have any experience with axigen.com or any of the above I listed?
Any help is much appreciated.