Mail Flow Overview

Mail Flow Overview

I  have outlined the brief overview of the mail flow in exchange 2007. In order to understand the mail flow , we need to know few components of the exchange. They are :

• Send Connector
• Receive connector
• Hub Transport Role and its component involved in mail flow.

Mail flow will take place with the help of SMTP connectors. These SMTP connectors will handle all the inbound and outbound mail flow. SMTP connectors  are the exchange components that support one-way smtp connections. Since these can handle only one way, there are two connectors one for sending –Send Connector and the other to receive –Receive connector.

            Receive Connector: This connector is required by exchange to accept any smtp connection. This connector will enable Hub Transport server or edge transport server to receive email from any smtp server on internet , other HTS . Multiple receive connectos can be configured on a single server. There is no need to create receive connectos to route mails between hts servers within the same forest.

Send Connector: This is required to send smtp mail to any smtp server on internet or another smtp server within the same organization. 

Both the above connectors can be configured using Exchange management console.

Hub Transport Role: This is one of the Role of MS exchange 2007 responsible for mail flow. The service called Exchange Hub Transport  service(msexchangetransport.exe) will be running on Hub transport server. Below are the components of HTS involved in mail flow:

• Submission Queue : Mails to be routed will be residing in this queue.
• Store Driver : This is responsible for retrieving mails from the client and involves in format conversion of the mail.
• Microsoft Exchange Mail Submission Service : This is a notification service that alerts HTS to pick mail.
• Pickup Directory :  This is a directory which will be forwarding mails to submission queue with the help of categorizer
• Categorizer : This components is responsible for identifying the route of the emails i.e internal or external. Categorizer  will be performing the below tasks:
• Identification and verification of recipients
• Expansion of distribution lists
• Determination of routing paths
• Conversion of content formats
• Application of message policies

Mail flow Process:

When a mail is sent from outlook below are the steps performed on the server:

• ·         When a mail is sent, store driver on the HTS server retrieves it from outlook client and transfers it to submission queue. When this happens mail is moved from senders outbox to Sent items.
• ·         The Microsoft Exchange Mail Submission Service is a notification service that runs on Mailbox server roles. It notifies the Hub Transport server role to pick up the message from the sender’s Outbox.
• ·         Each message that is transferred to the pickup directory has been successfully submitted to the submission queue via the categorizer. Messages placed in the Pickup Directory must be in the appropriate format(Messages will be in MAPI format and will be converted to Summary Transport Neutral Encapsulation Format (S/TNEF) before being placed in the Submission Queue. If the conversion fails, a NDR will be generated. This is done by Store driver) and have read/write permissions configured. It allows you to take a properly formatted text file and have the Hub Transport server role process and deliver it.
•  ·         The categorizer always picks the oldest message from the Submission queue and checks whether this message has to be routed internally in the Exchange organization or externally.