MTA

The MTA routes messages among Microsoft Exchange Server computers within a site and to MTAs in other sites. It also expands distribution lists. The MTA uses a memory cache for increased performance.

When the MTA receives a message, it performs the following tasks:

• Secures the message in the message transfer database and queues the message until it can be sent.
• Queries the directory to determine where the message should be routed.
• Routes the message to the MTA of the recipient's server or to the information store for local delivery or delivery through a connector.
• Deletes the message after it is routed.

The MTA uses two types of X.400 interfaces when routing messages:

• The message access (MA) Interface is used between X.400 clients and X.400 MTAs. The MTA uses this interface to communicate with the other Microsoft Exchange Server components.
• The message transfer (MT) Interface is used between X.400 MTAs. The MTA uses this interface to communicate with other Microsoft Exchange Server MTAs and X.400 compatible MTAs.

Administrators and applications have access to the MTA.

Administrators Administrators have access to the MTA through the Administrator program, and they have permission to perform the following tasks:

• Set the MTA name or password.
• Set limits on message sizes.
• Recalculate the routing tables.
• Configure distribution list expansion.

Applications Other applications running on Windows NT Server have access to and are accessible by the MTA. The MTA has access to the directory, information store, and system attendant to perform the following tasks:

• Requesting address information from the directory when it must resolve addresses or expand distribution lists
• Sending log entries to the system attendant for message tracking
• Delivering messages received from remote MTAs to the local information store
• Routing messages from the local information store to remote MTAs