The most common way of configuring Exchange Server to receive SMTP email is to set up an MX record for the company's domain that points to the company's public IP address. Usually, a firewall is then configured to route inbound SMTP traffic to the company's Exchange server.
Sometimes, though, this type of configuration isn't an option for an organization, particularly smaller businesses. For example, in some locations, such as where I live, it is impossible to get a public IP address. The expense of leasing a public IP address, and the necessary hardware investments, are other factors that can put this option out of reach for many one-man shops and smaller companies.
If you are in a situation that makes hosting your own externally accessible Exchange Server impossible, you're not out of luck. There is a way to route inbound SMTP email through your Internet Service Provider (ISP) and then have it delivered to an Exchange server that is not directly accessible from the Internet.
For the purposes of this article, I will treat your ISP as though it is configured to act as an Exchange Server smart host. The smart host's job is to queue inbound SMTP messages. Your Exchange Server would then connect to the smart host at periodic intervals and pull the queued messages using either ETRN or TURN commands.
What this means is that email messages that are destined for your domain actually go to one of your ISP's email servers. Your Exchange server then downloads the messages and places them in the appropriate mailboxes.
The ETRN/TURN configuration process
What if the SMTP connector does not exist?
Depending on how your Exchange Server organization is configured, you may or may not initially have an SMTP connector available to you. If there is no pre-existing SMTP connector, you will have to create one:
What if broadband Internet connectivity is not available?
You can get around the problem of limited or u
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navailable broadband connectivity by configuring Windows Server 2003 to act as a demand-dial router. A demand-dial router is a router that detects the absence of a connection to a specific resource (in this case, your ISP), and therefore uses a modem to establish temporary connectivity.
Before I show you this technique, I should mention that you should not configure demand-dial routing directly on your Exchange server for security and performance reasons. It's best to install a copy of Windows Server 2003 onto an old PC, connect a modem to the PC, and use that as your demand-dial router (assuming that a new server isn't in the budget).
Configuring demand-dial routing
Your demand-dial interface is ready to go!
About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Exchange Server, and has previously received Microsoft's MVP award for Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at http://www.brienposey.com.
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Tip: Free open-source SMTP/POP3 email for Windows
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Expert Advice: Send and retrieve Exchange Server email through POP3
Tip: Many ISPs now blocking port 25
FAQ: Exchange and Small Business Server issues
Reference Center: Exchange Server mailbox management tips and resources
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