Notes from the Lab

Exchange 2007: Mailflow Changes

June 13th, 2006

Here is what I understand so far.

No Routing Groups, No Link State, No Connectors

There is no Routing Group in Exchange 2007. To some degree that functionality has been replaced by AD site. Essentially, Exchange 2007 doesn’t have its own topology. It uses AD Topology to calculate routes, connection costs etc.

Send It Directly

In Exchange 2003, the only case when mail gets sent directly from one server to another is when they are in the same Routing Group. Between Routing Groups, they use Bridgeheads. Furthermore, if there is no direct Routing Group Connectors, several Bridgeheads get involved. All of this stops with Exchange 2007. By default, every Exchange server, that can send e-mail (I will explain this one below) sends mail directly to the recipient server (actually, to the server, closest to the recipient, that is capable of receiving mail, but again, I’ll explain it below) no matter how far away it is. Even if there is no direct site link between sites. In Exchange 2003 terms, all the transport-enabled servers in Exchange 2007 Organization behave as if they were one large Routing Group. You can change it by specifying “hub sites”. In this case, if there is no direct link between sites, Exchange will use servers in a “hub site” for relay.

Store or Send

In Exchange 2003 mailbox servers send and receive mail. In fact, the only servers that don’t send or receive mail are the servers that don’t have mailboxes: front-end servers, public folder servers, etc. In 2007 mailbox servers and transport (”hub”) servers are separate. You can have them on one physical machine, but those are two distinct software components. In essence the process of transporting e-mail is the following:

1. User hits Send
2. Mailbox server signals closest hub server that it has mail to send. Closest hub server is calculated based on AD sites topology.
3. Hub server establishes MAPI connection to the mailbox server and retrieves mail
4. Hub servers sends mail (using SMTP) to the hub server closest to the recipient’s mailbox server. That is if it’s a different hub server.
5. This second hub server uses MAPI to put mail int the recipient’s mailbox.

BTW, all the network traffic in the process above is encrypted. It’s either encrypted RPC or TLS SMTP. This server is the same even if you send mail to the same mailbox server or even to yourself

Entry Filed under: Exchange