It's true that in the US it's a bit less known but if you want to talk about complete and Enterprise ready Collaboration Platform then you should have a look at Zarafa: http://www.zarafa.com/
It's not just perfect as a MS Exchange replacement which uses a fraction of the resources and costs, it also includes video conferencing, instant messaging, file sharing, email encryption, etc...
Have you tried OwnCloud integrated with Zarafa?
I think is the best alternative to Office365 and Google Apps as you get all the MS Exchange features on your RedHat server and with OwnCloud you can manage and files and attachments.
Authored Comments
It's true that in the US it's a bit less known but if you want to talk about complete and Enterprise ready Collaboration Platform then you should have a look at Zarafa: http://www.zarafa.com/
It's not just perfect as a MS Exchange replacement which uses a fraction of the resources and costs, it also includes video conferencing, instant messaging, file sharing, email encryption, etc...
Have you tried OwnCloud integrated with Zarafa?
I think is the best alternative to Office365 and Google Apps as you get all the MS Exchange features on your RedHat server and with OwnCloud you can manage and files and attachments.