Understanding the Basics of E-mail Routing

Exchange uses e-mail addresses to route messages to mail servers inside and outside the organization. When routing messages internally, Hub Transport servers use mail connectors to route messages to other Exchange servers, as well as to other types of mail servers that your company might use. Two standard types of connectors are used:

• Send connectors

• Receive connectors

Send and Receive connectors use Simple Mail Transfer Protocol (SMTP) as the default transport and provide a direct connection among Hub Transport servers in an organization. Hub Transport and Edge Transport servers can also receive mail from and send mail to other types of mail servers.

You can use these connectors to connect Hub Transport servers in an organization. When routing messages outside the company, Hub Transport and Edge Transport servers use mail gateways to transfer messages. The default gateway is SMTP.

Exchange Server 2007 uses directory-based recipient resolution for all messages that are sent from and received by users throughout the organization. The Exchange component responsible for recipient resolution is the Categorizer. The Categorizer must be able to associate every recipient in every message with a corresponding recipient object in Active Directory.

All senders and recipients must have a primary SMTP address. If the Categorizer discovers a recipient that does not have a primary SMTP address, it will either determine what the primary SMTP address should be or replace the non-SMTP address. Replacing a non-SMTP address involves encapsulating the address in a primary SMTP address that will be used while transporting the message.

LOS 3-1-A-a 

Non-SMTP email address formats include fax, X.400, and messages originating from Lotus Notes. The Categorizer encapsulates e-mail addresses using non-SMTP formats in the Internet Mail Connector Encapsulated Addressing (IMCEA) format. For example, the Categorizer encapsulates the fax address, FAX:[phone] as [e-mail]. Any e-mail address that is longer than what SMTP allows is transmitted as extended properties in the XExch50 field.

In addition to primary SMTP e-mail addresses, you can configure alternative recipients and forwarding addresses for users and public folders. If there is an alternative recipient or forwarding address, redirection is required during categorization. You specify the addresses to which messages will be redirected in Active Directory, and redirection history is maintained with each message.