Saturday, August 19, 2017
Home > Exchange > Exchange 2007 Mail Flow Facts

Exchange 2007 Mail Flow Facts

Mail flow is termed as a movement of incoming and outgoing mail within an Exchange organization. In Exchange 2007, all mails are routed (including mail sent and received on the same Mailbox server) through a Hub Transport server before it is delivered to a Mailbox server. All external mail must additionally go through an Edge Transport server. The use of transport servers for all mail delivery allows you to apply transport rules to mail, regardless of its origin or destination. With these rules you can control delivery or apply filters, such as anti-spam and antivirus, to all mail.

Exchange transport servers use connectors to define how inter-server communication takes place. The connector describes how the transport servers communicate with other transport servers, with legacy Exchange servers, with other messaging systems, and with devices on the Internet. There are three types of connectors:

  • Send connectors control outbound communications.
  • Receive connectors control inbound communications.
  • Foreign connectors control outbound communications with servers that do not use SMTP for communication.

The following table describes how messages are routed in various scenarios.

Local Mail Flow

If a user sends a message to another user whose mailbox resides on the same server, the following steps are performed:

  1. The message is received by the Mailbox server.
  2. The Mailbox server submits the message to the Hub Transport server using RPC.
  3. The Hub Transport queries the Domain Controller or the Global Catalog server to determine the location of the recipient and a method of delivery.
  4. The message is forwarded to the user’s mailbox on the Mailbox server.
  5. The recipient is notified of new mail.
Inbound Mail Flow

Inbound mail flow are messages that have been received from the Internet. In a typical inbound mail flow scenario, the following steps take place:

  1. A message is received by an Edge Transport server from an external host using SMTP over port 25.
  2. The Edge Transport server verifies that the address is a valid address in the organization then applies message hygiene (such as antivirus and anti-spam scans) to the message.
  3. The Edge Transport server transfers the message to a Hub Transport server using SMTP over port 25.
  4. The Hub transport server queries the Domain Controller to locate the recipient’s mailbox.
  5. The Hub Transport server communicates with the Mailbox server using MAPI and RPC and delivers the message.

Note: It is possible to deploy an Exchange environment without deploying an Edge Transport server. If you choose to create an environment without an Edge Transport server, you can choose to deploy the anti-spam and antivirus agents found on the Edge Transport server on the Hub Transport server instead.
Outbound Mail Flow
Outbound mail flow represents messages that are sent to an external entity, such as Internet recipients. In a typical outbound mail flow scenario, the following steps take place:

  1. A message is received by the Mailbox server.
  2. The Mailbox server sends the message to the Hub Transport server using RPC.
  3. The Hub Transport server recognizes that the recipient is an external recipient and checks to see where to forward the message. If an Edge Transport server is present in the environment, then there will be a Send connector that identifies the Edge Transport server. The Hub Transport server sends the message to the Edge Transport server using SMTP over port 25.
  4. The Edge Transport server will do one of the following, depending on its routing configuration:
    • If it is configured with a Send connector that uses another smart host (such as an e-mail server at your ISP), it will forward the message on to the alternate smart host.
    • If it is configured to route messages using a DNS server:
      1. The server queries the DNS server for an MX record that identifies the server(s) which are responsible for managing e-mail for the recipient domain.
      2. The DNS server provides the Edge Transport server with the IP address and the name of the recipient mail server.
      3. The Edge Transport server initiates a connection to the remote SMTP server using port 25.
Remote (Inter-site) Mail Flow
Remote mail flow represents messages that are being sent to other Exchange servers but are located in different sites. The following scenario demonstrates the default behavior of how Hub Transport servers relay messages between sites:
  1. A message is submitted by a user to the local Mailbox server.
  2. The Mailbox server submits the message to the Hub Transport server using RPC.
  3. The Hub Transport server categorizer queries the Global Catalog server to identify the site location of the recipient’s Mailbox server.
  4. The Hub Transport server sends the message to the destination site.
  5. A Hub Transport server in the destination site receives the message, then forwards it to the appropriate Mailbox server.

Inter-site mail delivery typically uses implicit (automatic or built-in) Send connectors to identify the destination mail servers

Leave a Reply

Your email address will not be published. Required fields are marked *

four × three =