SMTP provides two communicate with each other SMTP session how to exchange information between.
SMTP process is responsible for sending mail is SMTP client , is responsible for receiving mail process SMTP server .
SMTP command specifies 14 (letters), and 21 kinds of acknowledgment information (simple three-digit code + text).
TCP port number 25, C / S
SMTP traffic three stages:
[Test] does not require such careful
SMTP's shortcomings:
1.SMTP not send executable files or other binary objects.
2.SMTP only transmit 7-bit ASCII, can not send text other non-English speaking countries.
3.SMTP server will reject mail over a certain length.
Common Internet Mail Extensions MIME:
The e-mail system can support voice, image, video, and so on a variety of national languages.
So that the transmission was rich in content!
Post Office Protocol the POP3:
the TCP port number 110 C / S
Internet message access protocol IMAP:
IMAP protocol complex than the POP protocol. When the IMAP client program on a user's mailbox Pc open IMAP server, the user can see the header mailbox,
if the user needs to open a message, the message was uploaded to the user's computer.
IMAP allows users to use different computers in different places at any time online reading mail, are also allowed to read only a certain part of the message
(look at the body, then there is WiFi when downloading attachments).
Web-based e-mail [commonly used]
