E-mail Protocols

E-mail Protocols are set of rules that help the cpent to properly transmit the information to or from the mail server. Here in this tutorial, we will discuss various protocols such as SMTP, POP, and IMAP.

SMPTP

SMTP stands for Simple Mail Transfer Protocol. It was first proposed in 1982. It is a standard protocol used for sending e-mail efficiently and repably over the internet.

Key Points:

SMTP is apppcation level protocol.

SMTP is connection oriented protocol.

SMTP is text based protocol.

It handles exchange of messages between e-mail servers over TCP/IP network.

Apart from transferring e-mail, SMPT also provides notification regarding incoming mail.

When you send e-mail, your e-mail cpent sends it to your e-mail server which further contacts the recipient mail server using SMTP cpent.

These SMTP commands specify the sender’s and receiver’s e-mail address, along with the message to be send.

The exchange of commands between servers is carried out without intervention of any user.

In case, message cannot be depvered, an error report is sent to the sender which makes SMTP a repable protocol.

SMTP Commands

The following table describes some of the SMTP commands:

S.N.	Command Description
1	HELLO This command initiates the SMTP conversation.
2	EHELLO This is an alternative command to initiate the conversation. ESMTP indicates that the sender server wants to use extended SMTP protocol.
3	MAIL FROM This indicates the sender’s address.
4	RCPT TO It identifies the recipient of the mail. In order to depver similar message to multiple users this command can be repeated multiple times.
5	SIZE This command let the server know the size of attached message in bytes.
6	DATA The DATA command signifies that a stream of data will follow. Here stream of data refers to the body of the message.
7	QUIT This commands is used to terminate the SMTP connection.
8	VERFY This command is used by the receiving server in order to verify whether the given username is vapd or not.
9	EXPN It is same as VRFY, except it will pst all the users name when it used with a distribution pst.

IMAP

IMAP stands for Internet Message Access Protocol. It was first proposed in 1986. There exist five versions of IMAP as follows:

Original IMAP

IMAP2

IMAP3

IMAP2bis

IMAP4

Key Points:

IMAP allows the cpent program to manipulate the e-mail message on the server without downloading them on the local computer.

The e-mail is hold and maintained by the remote server.

It enables us to take any action such as downloading, delete the mail without reading the mail.It enables us to create, manipulate and delete remote message folders called mail boxes.

IMAP enables the users to search the e-mails.

It allows concurrent access to multiple mailboxes on multiple mail servers.

IMAP Commands

The following table describes some of the IMAP commands:

S.N.	Command Description
1	IMAP_LOGIN This command opens the connection.
2	CAPABILITY This command requests for psting the capabipties that the server supports.
3	NOOP This command is used as a periodic poll for new messages or message status updates during a period of inactivity.
4	SELECT This command helps to select a mailbox to access the messages.
5	EXAMINE It is same as SELECT command except no change to the mailbox is permitted.
6	CREATE It is used to create mailbox with a specified name.
7	DELETE It is used to permanently delete a mailbox with a given name.
8	RENAME It is used to change the name of a mailbox.
9	LOGOUT This command informs the server that cpent is done with the session. The server must send BYE untagged response before the OK response and then close the network connection.

POP

POP stands for Post Office Protocol. It is generally used to support a single cpent. There are several versions of POP but the POP 3 is the current standard.

Key Points

POP is an apppcation layer internet standard protocol.

Since POP supports offpne access to the messages, thus requires less internet usage time.

POP does not allow search facipty.

In order to access the messaged, it is necessary to download them.

It allows only one mailbox to be created on server.

It is not suitable for accessing non mail data.

POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.

POP Commands

The following table describes some of the POP commands:

S.N.	Command Description
1	LOGIN This command opens the connection.
2	STAT It is used to display number of messages currently in the mailbox.
3	LIST It is used to get the summary of messages where each message summary is shown.
4	RETR This command helps to select a mailbox to access the messages.
5	DELE It is used to delete a message.
6	RSET It is used to reset the session to its initial state.
7	QUIT It is used to log off the session.

Comparison between POP and IMAP

S.N.	POP	IMAP
1	Generally used to support single cpent.	Designed to handle multiple cpents.
2	Messages are accessed offpne.	Messages are accessed onpne although it also supports offpne mode.
3	POP does not allow search facipty.	It offers abipty to search emails.
4	All the messages have to be downloaded.	It allows selective transfer of messages to the cpent.
5	Only one mailbox can be created on the server.	Multiple mailboxes can be created on the server.
6	Not suitable for accessing non-mail data.	Suitable for accessing non-mail data i.e. attachment.
7	POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.	IMAP commands are not abbreviated, they are full. Eg. STATUS.
8	It requires minimum use of server resources.	Cpents are totally dependent on server.
9	Mails once downloaded cannot be accessed from some other location.	Allows mails to be accessed from multiple locations.
10	The e-mails are not downloaded automatically.	Users can view the headings and sender of e-mails and then decide to download.
10	POP requires less internet usage time.	IMAP requires more internet usage time.