<P> Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called mail transfer agents ( MTAs ) ; and delivered to a mail store by programs called mail delivery agents ( MDAs , also sometimes called local delivery agents , LDAs ) . Accepting a message obliges an MTA to deliver it , and when a message can not be delivered , that MTA must send a bounce message back to the sender , indicating the problem . </P>
<P> Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called mail transfer agents ( MTAs ) ; and delivered to a mail store by programs called mail delivery agents ( MDAs , also sometimes called local delivery agents , LDAs ) . Accepting a message obliges an MTA to deliver it , and when a message can not be delivered , that MTA must send a bounce message back to the sender , indicating the problem . </P>
all email services are based on which software model
all email services are based on which software model
the Simple Mail Transfer Protocol
the Simple Mail Transfer Protocol