Server software used to send, receive, and store the e-mail of all users who have mail IDs in the organisation. Typically, depending on the actual size of the organization, the mail server software could either reside on a server or run off a normal PC. There are many different kinds of mail server software. Commercial options include Microsoft Exchange and Lotus Notes. On Linux there are a number of free mail server software available. Your choice would depend on the complexity of requirements. Consider whether the company’s e-mail needs to be administered centrally or whether each individual user will manage his own mailbox.