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Simple Mail Transfer Protocol (SMTP): The Internet standard protocol used to transfer electronic mail from one computer system to another.
Simple Mail Transfer Protocol (SMTP) is the default standard for email transmission across the Internet.
SMTP is a relatively simple, text-based protocol, where one or more recipients of a message are specified (and in most cases verified to exist) and then the message text is transferred. It is quite easy to test a SMTP server using the telnet program. SMTP uses TCP port 25. To determine the SMTP server for a given domain name, the MX (Mail eXchange) DNS record is used.
The SMTP mail transaction process itself consists of three steps:
Transaction Initiation and Sender Identification: The SMTP sender tells the SMTP receiver that it wants to start sending a message, and gives the receiver the e-mail address of the message's originator.
Recipient Identification: The sender tells the receiver the e-mail address(es) of the intended recipients of the message.
Mail Transfer: The sender transfers the e-mail message to the receiver. This is a complete e-mail message meeting the RFC 822 specification (which may be in MIME format as well).
IMAP:
Internet Message Access Protocol (IMAP) is a mail protocol that provides management of received messages on a remote server. The user can review headers, create or delete folders and messages, and search contents remotely without having to download the mail. It includes more functions than the similar and popular POP mail protocol.
IMAP is gradually replacing POP as the main protocol used by email clients in communicating with email servers. Using IMAP an email client program can not only retrieve email but can also manipulate message stored on the server, without having to actually retrieve the messages. So messages can be deleted, have their status changed, multiple mail boxes can be managed, etc. IMAP is defined in RFC 2060.
