What is SMTP?

Simple Mail Transfer Protocol: The Internet standard protocol for transferring electronic mail messages from one computer to another. SMTP specifies how two mail systems interact and the format of control messages they exchange to transfer mail.

What is POP3?

POP3 is a commonly implemented method of delivering email from the mail server to the client machine. Other methods include IMAP and Microsoft Exchange. The POP3 server specified in a person's email program specifies where to look for email that is directed to a particular email address. This should never be changed unless told to by the ISP or company IT department that provides the email address. ...    

What is IMAP?

Internet Message Access Protocol'. IMAP is a method of distributing e-mail. It is different from the standard POP3 method in that with IMAP, e-mail messages are stored on the server, while in POP3, the messages are transfered to the client's computer when they are read. Thus, using IMAP allows you to access your e-mail from more than one machine, while POP3 does not. This is important because some email servers only work with some protocols.

What is an Email client ?

An email client (or mail user agent [MUA]) is a computer program that is used to read and send e-mail. Protocols supported by email clients include POP3 and IMAP. 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 SMTP protocol is used by most email clients to send e-mail.

Common Email client

Microsoft Outlook	Outlook Express	Eudora
Netscape Mail	Mozilla	Thunderbird