A message, either submitted by a client or sent from another server, comes in through the designated TCP port (the default port is 25). It is placed in the Queue directory.
If the recipients are local, the message is transferred from the Queue directory to the mailbox store. Once the message is deposited in the store, the SMTP delivery cycle is complete.
If recipients are not local, the message is processed for remote delivery.Enlarge figure
Note Messages can also be delivered by copying them to the Pickup directory.
Related TopicsIntranet-to-Internet Communication