Saturday, May 1, 1999

Intelligent front-end hosts for SMTP


By Ron Herardian

This article is the second in a three-part series covering Domino and Internet email. Last month I explained capacity planning issues for Internet email. This month's article describes front-end solutions that allow centralization of SMTP services and that ease migration to Domino from cc:Mail.

Internet email is not what it used to be. Medium and large sized companies today have to deal with multiple DNS domains, multiple languages (character sets), multiple Internet address formats, migration issues, spam, and directory synchronization issues. Managing Internet email can be complex and companies are often at a loss for ways to deal with these things. The answer, however, is much less complex than the problem: install an intelligent front-end host to process and route inbound Internet email. The power and architectural simplicity of this solution will become apparent as we look at the different problems that are all solved by this solution.

An intelligent front-end solution for SMTP means that inbound SMTP email is received by a mail host that forwards mail to various MTAs or gateways. Typically this means receiving email from the Internet and forwarding it to other systems through a private WAN. The simplest implementation of this kind would use Berkeley sendmail and a simple alias file. A more sophisticated version would do the following:

  • Handle email for multiple DNS domains and address formats;
  • Handle mail spanning multiple languages and character sets;
  • Handle email migration issues;
  • Provide industrial-strength anti-spam capabilities;
  • Synchronize directory information with Domino and possibly other systems.

The same host may also serve as an outbound SMTP relay but this is standard functionality in sendmail so we won't spend any time looking at outbound Internet email. There may be one or many points at which mail exits an organization's WAN.

In last month's article I wrote about the rapid growth of Internet email and the challenges that it presents for administrators. Rapid growth in Internet email increases the administrative burden and creates pressure to centralize SMTP services. Centralization of SMTP services means that mail hosts must be able to handle multiple Internet domains and languages.

Multiple DNS domains: The Internet perspective

Nearly every company has to deal with multiple DNS domains. The reason why this is important is that companies want to standardize their Internet address format or limit the number of address formats. First we'll want to deal with the mechanics of this from the Internet point of view and then from the Domino point of view. It is important to note that the SMTP and DNS technologies allow mail for a given domain to be routed only to one primary point for that domain. In general, Internet mail is not routed based on the user ID (an exception is source routing).