= Glossary

[[email_client]]
Email Client::
Any software application that acts as a POP Client or an IMAP Client.

xref:messages/imf.adoc[IMF]::
*Internet Message Format* (IMF) is the base specification that defines the
syntax of an email message.

[[email_server]]
Email Server (or Mail Server)::
Any host that contains a sofware application that acts as a POP Server, an
IMAP Server, or an MTA.

IMAP::

IMAP Client::
One of the main actors in an email system that implements the IMAP protocol. The client
acts as a slave, in that it mirrors the state of the IMAP Server.

IMAP Server::
One of the main actors in an email system that implements the IMAP protocol. The server
acts as the master, in that it dictates the state that will be seen on each of the
IMAP Clients.

JMAP::

xref:messages/mime.adoc[MIME]::
*Multipurpose Internet Mail Extension* (MIME) is a specification that extends
IMF, defining most of the "advanced" features of email.

[[mta]]
MTA::
A *Mail Transfer Agent* (MTA) is a host that is capable of providing a mail
transport service compliant with the SMTP protocol.

MUA::
A *Mail User Agent* (MUA) is either an agent that hands over a message to an initial
MTA on the originating side of a transmission, or receives the message from the
final MTA on the terminating side of a transmission. It is in some respects similar to
an MTA, but is local in scope and does not necessarily follow a known specification.

xref:protocols/smtp.adoc[SMTP]::
*Simple Mail Transfer Protocol* (SMTP) is a protocol that specifies how to transmit
a valid email message from one MTA to another.

[[open_relay]]
Open Relay::

POP::

POP Client::
One of the main actors in an email system that implements the POP protocol. The client
is on the host that is closest to the user from a logical perspective, and is the host
to which messages are delivered from the POP Server.

POP Server::
One of the main actors in an email system that implements the POP protocol. The server
is part of the host that is logically farthest from the user. It is the host on which
the messages are initially delivered, and where they temporarily await collection by
the POP Client.
