Best practice for internal use

[Sascha Schneider]

Hi list, 

I want to replace our MS Exchange for it gives me multo problemos when trying 
to use it with other clients than outlook.
I tested some groupware and finally got to kolab.
Now I still have some questions for a setup on an internal server.

Situation:
- ISP with POP3 and webmail access + homepage under "ourdomain.be"
- internal ubuntu Server with Samba (not PDC --  YET) and Dovecot IMAP-Server 
with internal domain "administration.local" + second server MS with exchange.

So if I want to replace the existing MS Exchange I will have to use fetchmail 
to get the mails from the ISP into the users mailboxes.

Question:
- do I use the internal domain as primary domain "administration.local", 
ourdomain.be as secondary or the other way around??
- do I the use the other email as mailalias for each user??
- are there any other hints or howtos I have to check to not run into 
problems??

Greetings from belgium, Sascha