Exchange2000 to Linux based

[tickticker]

Hello everyone,

Been busy with a few contracts, but I'd like to ask the list for some 
suggestions/recommendations and leave a few comments of my own.

I have a client with over 1700 users on Exchange2000 and when I audited them, 
they only had 10 licenses... oops.  So I have them sold on going to the linux 
platform and using qmail or sendmail.  I think qmail would work fine, but 
they will be expanding up to 5000 users over the next couple years.  

Question: will this work on a single box reliably?  It's a dual 1.7 with a 
raid5 configuration and 1.2 gigs RAM.  Simple email is all it will do.

Question: Is there any conversion I can do or using tab delimited text files 
from active directory or is it a start from scratch proposition?  User names 
or accounts or even the mail files?

Comment: If there aren't then shouldn't there be?  I'm thinking of the admin 
with 1,000+ users saying "NO WAY am i going to do this conversion, It would 
take forever!"

Question: Anyone have experience doing this?  

Any help would be appreciated, expecially going forward.  While I will support 
a client's Microsoft base, I always recommend a Linux solution but this is 
the first Medium sized taker I've encountered.  Maybe someone knows of a 
knowledge base that tackles small, medium, large and enterprise class 
conversions ( Sales tactics, implementation, and client education )

Okay so my questions and comments are all mixed up, but I hope you get the 
gist of what I'm trying to find out here.

Again, ANY help is appreciated.  I am doing research on my own but the voice 
of experience is, to me, a better resource, expecially when geographically 
close.

Thanks in advance,

anthony