Friend of mine says ms exchange server is much faster and runs on less horsepower than previous RedHat server did. He's using active directory stuff, sql and outlook. Serving 300+ users using windows. Anyone with experience on this subject? Is there an open source solution that's equal to the job? The users really like the offsite access to mail and calendar features. Having never worked with this I couldn't suggest what would work. I'd like to come back at him with a solution to drool over.

I can only assume your friend has either:

a. Never used Linux
b. Has a HUGE MS server

We have an inhouse MS Exchange server and a LAMP server running Horde on RHEL5. The LAMP server also runs Samba.

Both have same number of users, around 145
Both give similar performance after upgrading the MS server to keep the MS users happy after seeing the performance of those using the LAMP server.

MS server is a quad quad core Xeon (16 cores) with 64GB RAM to achieve this performance.

LAMP server is a Core 2 Duo Pentium with 2GB RAM.

Speaks for itself.

So running horde and samba on rhel5 will give all the same services as exchange. Including the active directory and lookout/calendar etc..? equally as good on less hardware?

I think I'll go write down exactly what it is he's doing and get back to you. Not having worked around these toys is quite a bit different than reading about it.

Not entirely. Samba does not offer Active Directory services though there is work towards this in Samba 4.

We don't have a mixed network, instead we have 2 essentially separate networks. If we did need to link them, we would use the MS active directory and integrate Samba that way.

Our Horde users love the shared contacts and calendars being available from outside the office since they have the same interface and access as from within. The MS users have access to Exchange via OWA but don't have access to anything other than their own data whereas in the office they can access others calendars etc.