Linux, UNIX or 2003.dont try runnning a 500 client mail server on XP pro. It wont work.
but if you guys want commercial support, go for Redhat. IF you cant afford redhat, get CentOS (free) - no support but the upside of it is that most techies know redhat, and there identical, so if you have major problems, you can get help from an independant source.
is for a internal issue report so when emplo. have issue will send it to this e-mail server....
Ok now I read this 2 ways, one is a helpdesk type of ticketing system, and the second it a secondary email system that is secure to internal lan only.
For 500+ people you really need a server setup and NOT to use XP at all. Depending on your experience level, you can go with a Linux server (RedHat, SuSE, Fedora for example) and there is lots of free software for that OS that can be used. Other wise will need a windows server with Exchange or some other type of email server software.
At this point it depends on who is going to administer the server and the accounts, and what type of OS are they used to working on.