Mail clients

E-mail messages are generally sent to an e-mail server that stores received messages in the recipient’s  e-mail mailbox.  The user later retrieves these messages with either a web browser or an e-mail  client that uses one of a number of e-mail retrieval protocols.  There are different types of mail clients protocol used to retrieve the user’s mail account from mail server they are

• Post office protocol
• Internet Message Access Protocol

2.5.1 Post Office Protocol

POP is one of the email client uses TCP/IP Protocol.  The design of POP3 and its procedure supports  end-users with intermittent connections (such as dial-up connections), allowing these users to retrieve  e-mail  when connected.

Post Office Protocol (POP)

Although most clients have an option to leave  mail on server, e-mail clients using POP generally connect, retrieve all messages, store them on the user’s PC as new messages, delete them from the server, and then disconnected.  The  main disadvantage of POP is the mail gets scattered wherever they access their account.

2.5.2 Internet Message Access Protocol

IMAP  supports both connected (online) and disconnected (offline) modes of operation.  E-mail clients using IMAP  generally leave messages on the server until the user explicitly deletes them.  This and other facets of IMAP  operation allow multiple clients to access the same mailbox.  Most e-mail clients support either POP3 or IMAP to retrieve messages; however, fewer Internet Service Providers (ISPs) support IMAP.  IMAP4 offers access to the mail store; the client may store local copies of the messages, but these are considered to be a temporary cache;   the server’s  store is authoritative.

For example,  Microsoft’s Outlook client typically uses a proprietary protocol to communicate with an Exchange server as does IBM’s Notes client when communicating with a Domino server, but all of these products also support  SMTP,POP3,and IMAP4.  Support for the Internet standard protocols allows many other e-mail clients such as Pegasus Mail or Mozilla Thunderbird to access these servers and similarly allows the clients to be used with other servers.  E-mail clients can generally be configured to use either POP3 or  IMAP4 to retrieve e-mail and in both cases use SMTP for sending.

Internet Message Access Protocol (IMAP)

Nearly all subscribers to individual Internet service provider e-mail accounts access their e-mail with client software that uses POP.

IMAP is often used in large networks; for example, a college campus mail system.   IMAP allows users to access new messages instantly on their computers, since the mail is stored on the network.  With POP3, users either download the e-mail to their computer or access it via the web.  Both methods take longer than IMAP, and the user must either download any new mail or “refresh”  the page to see the new messages.

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