E-mail client
From Wikipedia, the free encyclopedia
An e-mail client, also called a Mail User Agent (MUA), is a computer program that is used to read and send e-mail.
Originally, the MUA was intended to be a simple program to read the user's mail messages, which the mail delivery agent (MDA) in conjunction with the mail transfer agent (MTA) would transfer into a local mailbox.
(Note: SMTP did not originally use the term "MTA" until X.400 popularized the term and SMTP was no longer "simple.")
The most important mailbox formats are mbox and Maildir.[citation needed] These rather simple protocols for locally storing e-mails make import, export and backup of mailfolders quite easy.
E-mails to be sent would be handed over to the MTA, perhaps via a mail submission agent, therefore an MUA would not have to provide any transport-related functions.
Since the various Microsoft Windows versions intended for home use never provided an MTA, most modern MUAs have to support protocols like POP3 and Internet Message Access Protocol (IMAP) to communicate with a remote MTA located at the e-mail providers machine.
IMAP and the updated IMAP4 are optimized for storage of e-mail on the server, while the POP3 protocol generally assumes that the e-mail is downloaded to the client. The Simple Mail Transfer Protocol (SMTP) is used by most e-mail clients to send e-mail.
In addition to the fat client e-mail clients, or small MUAs in cooperation with a local MDA/MTA, presented here, there are also Web-based e-mail programs called webmail.
An important standard supported by most e-mail clients is MIME, which is used to send binary file e-mail attachments. Attachments are files that are not part of the e-mail proper, but are sent with the e-mail.
Messaging Application Programming Interface (MAPI) is a proprietary Microsoft Windows application programming interface (API) that can be used to access the Microsoft Exchange e-mail server or to interact with the Microsoft Outlook client.
