When a message is routed to a connector that fails to connect to the other MTA, the retry count is incremented and the MTA attempts to reroute the message. When a message is rerouted, the MTA performs routing and selection again to find the most efficient connector. A retry count is stored on each message for each connector that has been tried. If the message cannot be delivered after all the connectors have been tried, the message is returned with an NDR.
The maximum number of transfer retries and transfer interval are controlled by settings in the Override property page for the Site Connector, Dynamic RAS Connector, and X.400 Connector. These settings determine how many times and at what interval the MTA sends a message through the connector.
When a message is sent to a connector or gateway for a foreign system, such as the Microsoft Mail Connector or Internet Mail Service, the MTA considers the message delivered when it reaches the connector. Rerouting does not occur, even if the foreign system connector cannot deliver the message.
A message routed to a connector with an activation schedule of never active or remote initiated is not rerouted unless the activation schedule is changed while the message is waiting to be delivered.