About E-mail client…

November 20, 2007

Here is the definition: an email client is a frontend computer program used to manage emails. The email client may be any agent action as a client on an email server.

Functionality and Configuration

Retrieving messages from a mailbox

In this article a MUA refers to a Mail User Agent which is active when a user runs it. Messages arrive through the MTA (Mail Transfer Agent).

How it works? An user log on the server and runs a MUA - which will read messages - on the machine. MDA (Mail Delivery Agent) is used by MTA to add messages to that storage, possibly in concurrence with the MUA. This situation is a shared disk access, but a server can also benefit from direct disk access.

An user, in front of his personal computer, connects to a remote mailbox to retrieve messages. A client can download messages using POP (Post Office Protocol). Also, the clients can keep messages on the server with the IMAP (Internet Message Access Protocol).

Both POP and IMAP clients can be configured to access more mailboxes at the same time.

Formatting messages

Mail users agents comes with the ability of displaying and formatting texts. To, Cc, and Bcc are the destination fields, From is the author address, Sender in case there are more authors, and Reply-To in case responses should be addressed to a different mailbox.

Submitting messages to a server

An important function of a MUA is introducing new messages, connecting to MSA or MTA variations of the SMTP Protocol. The client want his message to be immediately delivered, without worrying how it is sent. Here comes the question: how does the server know whether to accept and relay submissions from that client? There are two possible ways. The first method recognizes the client’s IP address (because the client is on the same machine or because the client’s IP address is controlled by the same internet service provider that provides both internet access and mail services). The other method, since the SMTP protocol has an authentication extension, is to authenticate.

For a client there are settings required: the IP address, the port number, the user name and password for the authentication.

Standards

We know that the usual protocol used for sending email is SMTP (Simple Mail Transfer Protocol).

There is another important standard supported by most e-mail clients named MIME which is used to send email attachments. Attachments are not part of an email but are sent in the same time with the email.

The protocols used for incoming mails are: POP3 and IMAP4, for outgoing mails: SMTP and MSA.