Pick a package. Install for your server's distribution. Configure. Enjoy.
Since email was one of the original top-5 internet applications, you will find more
than plenty of readings about mail server operations and configuration online
using your favorite search engine.
Do some reading. While not gold medal complete and accurate, the Wikipedia article offers some nice background and vocabulary.
http://en.wikipedia.org/wiki/Email
Which of the several "mail server" packages are you planning to deploy? It is far easier to answer questions about a specific package than your general plea for help. (If you don't know about the variety of email server packages, you have homework to do.) All mostly work for main stream email. The troubles come on the edges of capacity (how many connections in simultaneous active use) and performance (how quickly does connection accomplish what it is asked to do).
If your organization is an 8-to-5, Monday-to-Friday enterprise, you will learn about
capacity on Monday morning when everyone logs in to get their email within a short
period of time. Another measure of capacity will become obvious when that 200 page
report is actually attached to 30 messages rather than placed somewhere shared and
folks get told where to fetch it.
There are also "Groupware" packages. These offer a collection of features and services designed around the collaboration and cooperation of typical office workers. These include email, calendar, address book, document sharing and related applications.
Some of these groupware packages include a set of servers to implement the basic features while other packages rely on whichever servers might be available on the machine where the groupware suite gets installed. Again, "which package" leads to meaningful questions and answers.
Another concern has little to do with the email server itself but the environment in which it is deployed. Many jurisdictions now require that a business entity maintain archives of messages according to regulations and laws. Have you done homework about those requirements at your enterprise? In many cases, this boils down to use of an archiving utility, managing those archives and associated media, and compliance documents.
Good Luck,
~~~ 0;-Dan
