Mailbox, also called mailbox, is one of the interpersonal communication tools. When the letter arrives, the recipient has no time to receive it in person because he is out or busy with other things. Only the mailbox will do it for him, and the recipient will open the mailbox when he is free, and the letter will be collected, opened and processed at one time. In order to show a unified image to the domestic public, postal administrations usually choose specific colors to make the public recognize their services as a whole.

Judging from the mainstream color of postal mailboxes in various countries, red is the most widely used color. The color of People's Republic of China (PRC)'s mailbox is green. With the popularization of modern Internet, e-mail has the function of storing and sending and receiving electronic information, and it is one of the most important information exchange tools on the Internet. The biggest feature of e-mail is that people can send and receive letters at any time, which solves the time and space constraints.

Security:

Transmission may be eavesdropped. In order to deal with this situation, there are two solutions:

Storage safety

For encrypted messages, you can choose not to save decrypted messages. Encrypted mail means that the sender encrypts the mail itself before sending it, rather than encrypting the transmission. If the message itself is encrypted, there is no need for encrypted transmission.

For unencrypted mail (meaning that the sender didn't encrypt the mail itself before sending it, whether to use encrypted transmission is another matter), the storage security of mail is just like the storage security of other files, and the key point is to prevent unauthorized use. Of course, just as ordinary files can be encrypted, these unencrypted emails can also be encrypted after they are received.

The receiver receives the acknowledgement.

The recipient may deny that he/she did not receive the email. In order to deal with this situation, different solutions have appeared, but there is no universally adopted solution. Microsoft Exchange Server of Microsoft Corporation provides delivery receipt. Because the machine sent "the recipient has received the confirmation", the recipient may have deleted the mail intentionally or unintentionally.

Denial of service attack

In order to prevent the user from using e-mail (for example, preventing her/him from receiving e-mail), a denial-of-service attack is to send a large amount of spam to the mailbox of the attacked user and fill it up.

In this way, the attacked users will not receive those useful emails. This security problem has been solved to a great extent. One is that the number of mailboxes is increasing, and the other is that mail service providers have provided some new filtering measures. Filtering measures sometimes treat useful e-mails as spam. At present, some mail service providers use body double Post to prevent external tracking of mail accounts.

Protocol for implementation

Common e-mail protocols are as follows: SMTP (Simple Mail Transfer Protocol), POP3 (post office protocol), IMAP (Internet Mail Access Protocol), HTTP, S/MIME. These protocols are defined by the TCP/IP protocol family.