Building a scalable e-mail solution

Planning your e-mail system for scalability will ensure that your mail administrators have to navigate fewer learning curves and your users experience less downtime later on. Here's how.

E-mail remains the true "killer app" of the Internet; most businesses have come to rely on it for exchanging quick, easy, unobtrusive communications with co-workers, customers, suppliers, partners and others.

Many small businesses start out using e-mail accounts available through their Internet Service Providers in the ISP's domain. As the business grows, you will probably create a Web presence and register your own domain (e.g., At that point, you'll want e-mail addresses in your domain, as well. Many ISPs will host your e-mail domain for an additional fee.

The advantage of this is that you don’t need someone on your staff who is tech savvy enough to run a mail server. The disadvantage is that you don’t have as much control over your mail services. For example, the ISP may use spam filters that rely on commercially available black lists, which often block entire domains because one user has been flagged as a spammer. This could prevent you from receiving mail from other, legitimate users of that domain.

The ideal situation is to be able to control your own filtering, be able to control other mail server settings (such as whether to allow attachments or HTML mail), and be able to make your own on-site backups of your users’ mailboxes in case of a server crash or other data loss. To do this, you’ll need to host your own mail server(s). But how can you get started without investing a big bundle of money, and still plan for growth from the small business to the enterprise level?

Components of an E-mail System

Sending and receiving e-mail seems pretty simple to users, but it requires a number of different components, working together:

  • Outgoing mail server: this is a server running the Simple Mail Transfer Protocol (SMTP) service that is used to send mail.
  • Incoming mail server: this is a server running either the Post Office Protocol v. 3 (POP3) or the Internet Mail Access Protocol (IMAP), which receives mail addressed to the user accounts configured on it.

E-mail client: this is the software installed on users’ computers that accesses the user’s mailbox on the POP3 or IMAP server to allow the user to read incoming mail, and provides an interface for composing mail and sending it through the SMTP server.

The outgoing and incoming mail server services can be installed on two different physical machines or on the same one.

Setting up your own SMTP Server

If you run a Windows Server operating system (NT 4.0 Server, Windows 2000 Server or Windows Server 2003), you don’t have to buy anything extra to set up an SMTP server to send mail for your organization. You can use the SMTP service that is part of Internet Information Services (IIS), Microsoft’s Web server program that’s included with the server OS.

Other popular SMTP servers include Sendmail and Qmail, which run on UNIX.

SMTP server software can also be installed on workstations to send mail directly from them without going through an ISP's SMTP server. This can be useful for laptop users when traveling. There are a number of free SMTP server programs designed for this purpose such as Softstack's Free SMTP, QK SMTP Server, PostCast SMTP Server, 1st SMTP Server from Axis Research, and many others.

Implementing a POP or IMAP Server

SMTP only gets you half-way there. You still need a way to receive incoming mail. You can set up a POP or IMAP server separately from your SMTP server, but there are many e-mail server solutions that incorporate both SMTP and POP and/or IMAP. These include Microsoft’s Exchange, Eudora Internet Mail Server, Mercury, Merak, XMail and others.

POP servers receive incoming e-mail over the Internet and store it on the server until the user downloads it to his/her client computer. The user processes the mail on the workstation (this is sometimes called offline processing). This works fine if the user always uses the same workstation, but not as well if the user needs to check mail from different machines. Because the mail is downloaded to the local computer, users can read or compose messages without being connected to the mail server. Most ISPs use POP for incoming mail.

IMAP servers receive incoming e-mail and store it in the user’s mailbox on the server. The user uses a mail client to view, read and respond to the mail, but the processing takes place on the server and the mail stays on the server. That means the user can access it again from any computer anywhere in the world. Many companies that run their own mail servers prefer to use IMAP for incoming mail. Many e-mail server packages support both POP and IMAP.

Growing your e-mail services with the business

If your business is growing rapidly, you’ll want an e-mail server solution that can expand to service a large number of users, and span multiple locations if the company adds branch offices that are geographically dispersed. Many mail server makers offer different editions of their software for different sized organizations. This makes it easy to upgrade without a steep learning curve that’s involved when you have to move to an entirely new software solution.

For example, Merak (made by IceWarp Software LTD) comes in three versions: Lite (supports up to 50 users and a single domain), Standard (supports multiple domains with up to 3000 users) and Professional (supports an unlimited number of domains and users and supports load balancing over multiple servers).

Microsoft’s Exchange Server 2003 comes in two editions: Standard (which provides for a maximum of 16 GB database size) and Enterprise (which provides for up to 16 TB database size).

Small businesses can also start out with Exchange at lower cost if they implement Windows Small Business Server (SBS) 2003, which includes Exchange in both its standard and premium editions.

Another consideration that may become important as the business grows is the ability to offer your company’s e-mail users a way to access their mail over the Web. This is a big advantage for those who must sometimes use public computers on which they can’t install or configure mail client software. Exchange, Merak, and other major e-mail packages include webmail functionality as part of the standard package or as add-ons.

Planning from the beginning for scalability can ensure that your mail administrators don’t have to start from scratch and learn new mail programs as the network grows, and that your users, who may rely heavily on their e-mail to get their jobs done, experience little or no "downtime."


Debra Littlejohn Shinder, MCSE, MVP is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. Deb is a tech editor, developmental editor, and contributor to over 20 add...