Thanks for the information.

About the administrating - we need so called 2-tier administration, because we will let our users to have their administrator, which will create, delete mailboxes, users and so on, we will give him some amount of space and different rigths. This tier must have nice web interface. Simple users will access their mailboxes with webmail software. 1-tier administrating - creating domains, asigned needed space - can be not implemented.

I hope, I described our needs. And I will check the sofware, which You recomend.