PostMaster Express is a LAN-based Mail Server. In a nutshell, it does the job of a POP Server and an SMTP server within a LAN. It simply replicates the Internet mail servers that help you send and receive mail across the Internet. You can now send and receive mail within your office network.

There are three types of mail in any organization – mail coming into the organization from the Internet (incoming), mail going out of the organization to others via the Internet (outgoing) and mail going from one colleague to another (internal or local). Let's look at each type of mail and see how they work.

Firstly, the mail server is installed on a machine which has Internet access. This could be through a dial-up or a leased line. A list of users (employees) is set up in the mail server. The Mail Server (let's say PostMaster Express) will communicate with the organization's POP accounts and download all mail. This is similar to how an email client contacts your personal POP account. In PostMaster Express's case, it works for the entire organization and downloads all the mail at one go.

Then it identifies the recipient of each mail with the list of users that are configured. Based on this, it sorts mail and stores the right mail in each user's mailbox. Users can then use any email client and access their mail. The POP account settings will be that of PostMaster Express machine. Thus, PostMaster Express removes the need of having a direct Internet connection on every desktop.

For each user, their SMTP server is PostMaster Express. They set up their email client such that when they send mails, the mails are delivered to the PostMaster Express's SMTP server. PostMaster Express puts them in a queue for onward delivery.

When PostMaster Express receives any mail for onward delivery, it will first check whether the recipient is an user configured. If it is, then it will deliver it to the appropriate user's mail box. If the user is not set up in PostMaster Express, then PostMaster Express will recognize the mail as an outgoing mail and put it in the outbound queue for uploading.

PostMaster Express will connect to the SMTP server of the ISP (with whom the company would have contracted) and send the mails for delivery to the intended recipients. The ISP's SMTP server would then take over as explained in the earlier chapters.

Thus a LAN-based server centralizes mail transfer in one machine connected to the Net. It allows organizations to give company email access to their employees without spending too much into giving Internet access to each one. With the facility of internal mail, intra-office communication becomes easy and efficient.

PostMaster Enterprise also works in a manner similar to PostMaster Express acting as Lan-based Mail Server. However, PostMaster Enterprise has much more advanced features which enable you exercise greater control over the functionality provided in PostMaster Enterprise.