<P> Email is submitted by a mail client ( mail user agent , MUA ) to a mail server ( mail submission agent , MSA ) using SMTP on TCP port 587 . Most mailbox providers still allow submission on traditional port 25 . The MSA delivers the mail to its mail transfer agent ( mail transfer agent , MTA ) . Often , these two agents are instances of the same software launched with different options on the same machine . Local processing can be done either on a single machine , or split among multiple machines ; mail agent processes on one machine can share files , but if processing is on multiple machines , they transfer messages between each other using SMTP , where each machine is configured to use the next machine as a smart host . Each process is an MTA ( an SMTP server ) in its own right . </P>
<P> Email is submitted by a mail client ( mail user agent , MUA ) to a mail server ( mail submission agent , MSA ) using SMTP on TCP port 587 . Most mailbox providers still allow submission on traditional port 25 . The MSA delivers the mail to its mail transfer agent ( mail transfer agent , MTA ) . Often , these two agents are instances of the same software launched with different options on the same machine . Local processing can be done either on a single machine , or split among multiple machines ; mail agent processes on one machine can share files , but if processing is on multiple machines , they transfer messages between each other using SMTP , where each machine is configured to use the next machine as a smart host . Each process is an MTA ( an SMTP server ) in its own right . </P>
which protocol is used to send email messages from a mail client to a mail server
which protocol is used to send email messages from a mail client to a mail server
SMTP
SMTP