[zillah]

Friend of mine works with an organization (50 users), they do not have Exchange server right now.

Right now they use virtual email accounts (not for all users) provided by telecommunication ISP.

They have their own domain, and I am not sure if they Active Directory or not

If they want to configure one of their stand alone server (windows 2003) as mail server, similar to link below
http://www.ilopia.com/Articles/Windo...ailServer.aspx

How many user accounts we can create with that stand alone box ? Is the stand alone box sufficient for 50 users accounts ?

Through my Google search I found only the link above with figures |(very useful) shows how to configure that ,,,is there any extra URL resources ?

Yes I am aware that there is alternate solutions, for instance this :
Kerio Technologies Inc. | Kerio MailServer - secure mail server for Windows, Linux & Mac OS X

[Law]

I am not familiar enough with Windows 2003 client access licensing but I am pretty sure there is no limit as to how many active directory users you can create as long as your hard drive space permits. However due to M$ CAL, you may need to buy additional licensing to support more users or device to connect simultaneously, as far as I'm aware, the standard version of 2003 only support 5 CALs. I stay away from M$ licensing by moving to Linux, you can run Postfix or free version of Open-Xchange for email server all equivalent to M$ without the licensing fee. However it takes more skill and time to do it in Linux.