Deploying Exchange Server 2013 : Exchange Server messaging roles (part 4) - Deploying Transport services: The essentials

The Transport service on Mailbox servers and the Edge Transport role perform similar tasks. You use both for messaging routing, and both have a similar set of filters to protect an organization from spam and viruses. The key difference is in where you place servers with these roles. You place a Mailbox server in the internal network and configure it as a member of the organizational domain. If you use a server with the legacy Edge Transport role, you place it in the organization’s perimeter network, and you do not configure it as a member of the organizational domain.

For computers with the Mailbox server or legacy Edge Transport role, the server cannot have the SMTP or Network News Transfer Protocol (NNTP) service installed separately. Although you install legacy Edge Transport servers outside the Active Directory forest, you must have a DNS suffix configured, and you must be able to perform name resolution from the legacy Edge Transport server to any Mailbox servers.

Both Mailbox servers and legacy Edge Transport servers can perform protocol logging and message tracking. Only Mailbox servers perform content conversion to format messages for recipients. Protocol logging allows you to verify whether a protocol is performing as expected and whether any issues need attention. Because this feature is designed for troubleshooting, it is disabled by default. Message tracking creates logs that track messages sent and received. Incoming mail from the Internet is converted to Summary Transport Neutral Encoding Format (STNEF) prior to being delivered. STNEF messages are always MIME-encoded and always have a Content-Transfer-Encoding value of Binary. Because content conversion is performed in the temp folder, you can improve performance by ensuring that the temp folder is not on the same physical disk as the paging file and operating system.

The transport pipeline used by Exchange 2013 is different from the transport pipeline for Exchange 2010 and has the following key components:

The Front End Transport service running on Client Access servers proxies all inbound and outbound SMTP traffic for Exchange 2013. Although the Transport service running on Mailbox servers performs nearly the same tasks as the Hub Transport role, it’s important to point out the differences. As with Exchange 2010, the Transport service handles all SMTP mail flow. The service also performs message categorization and message content inspection. Unlike Exchange 2010, however, the Transport service doesn’t communicate directly with mailbox databases. Instead, the Mailbox Transport Submission and Mailbox Transport Delivery services are used to provide separate mail submission and delivery processes.

The basic submission process works like this:

The basic delivery process works like this:

Messages from inside the organization enter the transport pipeline through a Receive connector, from the Mailbox Transport Delivery service, from the Pickup or Replay directories, or from agent submission. Messages from outside the organization enter the transport pipeline through a Receive connector in the Front End Transport service on a Client Access server and are then routed to the Transport service on a Mailbox server.

Unified messaging allows you to integrate voice mail, fax, and email functionality so that the related data can be stored in a user’s Exchange mailbox. To implement unified messaging, your organization must have a PBX that is connected to the LAN, and you must deploy Mailbox servers running Exchange Server 2013. After it is deployed, the Unified Messaging service running on a Mailbox server has the job of providing call answering, fax receiving, subscriber access, and auto-attendant features that allow access to content over the telephone and storage of content received from the PBX. However, it is the job of the Unified Messaging Call Router service running on Client Access servers to provide call routing and proxy services that allow calls to be connected.

Although some current PBXs, referred to as IP-PBXs, are Internet Protocol–capable, all other PBXs require a separate Internet Protocol/Voice over Internet Protocol (IP/VoIP) gateway to connect to the LAN. After you connect a PBX to the LAN, you can link it to Exchange by deploying and appropriately configuring the Unified Messaging service. The Desktop Experience feature, which is required to install Exchange server, provides the Microsoft Speech service, Microsoft Windows Media Encoder, and Microsoft Windows Media Audio Voice Code components used by the Unified Messaging service.

The Unified Messaging service doesn’t perform a great deal of I/O operations, and the primary potential bottlenecks for this service are the processors, memory, and network. Disk I/O operations for this service are primarily limited to accessing routing details and dial plans, which include auto-attendant and mail policy settings.

If you are planning to use Unified Messaging in a hybrid Exchange implementation, you’ll also need to configure session board controllers (SBCs). SBCs have two IP interfaces: one for your network and another that connects over the Internet. Your VoIP, IP-PBX, and SBC components must be configured to communicate with your Mailbox and Client Access servers. You also must create and configure a Unified Messaging IP gateway to represent each deployed device.