Unlike personal computers, these mail servers and their programs must run 24 hours a day, otherwise they cannot send and receive mail. Simple Mail Transfer Protocol SMTP and post office protocol POP are protocols responsible for sending and retrieving e-mail in client/server mode.
Extended data:
The e-mail client running on the user's computer requests the mail server to transmit the mail, and the mail server adopts the Simple Mail Transfer Protocol standard. Many mail transmission tools, such as outlook express, fox mail, etc. , comply with the SMTP standard and use this protocol to send mail to the mail server. SMTP protocol specifies the specific format of mail information and the management mode of mail.
Internet Information Access Protocol (IMAP) is a new protocol superior to POP. Like POP, IMAP can download mail, delete mail from the server or ask if there is any new mail, but IMAP overcomes some shortcomings of POP.
Baidu Encyclopedia-Email Protocol