Defining SMTP Dependencies

 

As discussed earlier in this chapter, Exchange relies on SMTP to deliver mail internally and externally. This means that, for Internet mail delivery, Exchange depends on SMTP. However, before configuring Exchange for Internet mail delivery, you must understand the components on which SMTP depends:

• Internet Information Services (IIS)

  As mentioned earlier, the SMTP service is installed as part of the Windows Server 2003 or Windows 2000 Server operating system. SMTP is a component of IIS and runs under a process named Inetinfo.exe. If you remove IIS from a server running Exchange, mail flow stops working.

  IIS provides a framework process for Internet services such as HTTP, SMTP, and Network News Transfer Protocol (NNTP). Do not confuse IIS with HTTP because several other services, such as SMTP, depend on IIS to function. After you install Exchange, the management of SMTP virtual servers moves to Exchange System Manager, even though the service itself continues to run in IIS. Because of this integration between Exchange and IIS, both the IIS component and the SMTP service that runs in IIS are required for Exchange and SMTP to function correctly.

• Active Directory

  Exchange Server 2003 is tightly integrated with the Microsoft Active Directory® directory service. Exchange stores all its configuration information in Active Directory, including information about recipient policies, SMTP virtual server configuration, and user mailboxes. However, SMTP reads its settings from the IIS metabase. Therefore, to supply IIS with the information it requires for SMTP functionality, Exchange System Attendant, using a component named DS2MB (directory service to metabase), replicates the configuration information from Active Directory to the IIS metabase.

• DNS

  SMTP depends on DNS to determine the Internet protocol (IP) address of its next internal or external destination server. Typically, internal DNS names are not published on the Internet. Therefore, SMTP must be able to contact a DNS server that can resolve external DNS names to send Internet mail, and also a DNS server that can resolve internal DNS names for delivery in the organization.

  Additionally, for your Exchange servers to receive Internet mail, your DNS server must contain a mail exchange (MX) resource record that points to the A record with the IP address of the SMTP virtual server on your Exchange server that receives Internet mail for your organization. If you are supporting multiple domains, an MX record must exist for each of these domains for DNS to accept mail for the domain.

• Recipient Policies

  Recipient policies establish the default e-mail addresses that use a specific protocol (such as SMTP) for a set of users. E-mail addresses define the valid formats for addressing inbound e-mail messages to the Exchange system. The default recipient policy sets the mail domain for which the virtual server accepts incoming e-mail messages. It specifies the default SMTP and X.400 addresses for all Exchange-based mailbox-enabled objects. You can also create additional recipient policies if your organization receives mail for multiple domains, or if your default domain is used strictly for internal purposes and you use a different external mail domain.

  Any SMTP domain specified in the recipient policies is replicated into the IIS metabase and set as authoritative local domains. Setting these domains as authoritative local domains means that SMTP accepts inbound mail for these domains and is responsible for sending all non-delivery reports for this domain. The only time an SMTP address is not considered local is when you add the address to the recipient policy because you clear the This Exchange Organization is responsible for all mail delivery to this address check box in the SMTP Address Properties dialog box.

  Installing and correctly configuring the previous components ensures that SMTP functions correctly with Exchange. With SMTP functioning correctly, you can focus on configuring SMTP to meet your organization's needs.