Email client sends message composed in client to Messaging Server Message Transfer Agent (MTA).
MTA requests verification of user ID and password from Directory Server.
Directory Server returns verification to MTA.
MTA checks Directory Server for the destination domain for each recipient.
Directory Server returns to MTA the destination domain for each recipient.
MTA forwards message to each recipient.
MTA forwards message to Messaging Server Message Store (STR) to store message in outbox.
MTA sends confirmation to email client.