Definition of IMAP4 protocol

The IMAP4 protocol is a revision of the IMAP protocol. The previous version is IMAP3. You may not be familiar with this agreement. However, in the past, this Protocol was widely used. Because we often use Outlook, it is closely related to this mail protocol.

Internet Message Access Protocol (IMAP) is an application layer Protocol used to Access local mail clients such as Microsoft Outlook, Outlook Express, Foxmail, and Mozilla Thunderbird) access emails on the remote server.

IMAP, POP3Protocol Of Post version 3, Post Office Protocol 3) is the most common Internet standard protocol for email access. In fact, all modern mail clients and servers support both. The current version of IMAP is "the first revision of the fourth version of IMAP" IMAP4rev1), which is defined in rfc3501.

IMAP, designed by Mark cripin, provides an alternative to the widely used POP3 mail protocol for mail access. Basically, both allow an email client to access the information stored on the email server. Some important aspects that only exist in IMAP include:

Supports connection and disconnection modes. When POP3 is used, the client will only connect to the server for a period of time until it downloads all new information, and the client will be disconnected. In IMAP, as long as the user interface is active and the content of the downloaded information is required, the client will be connected to the server all the time. For a large number of users, you can use the IMAP4 mode to get a faster response time.
Multiple customers can connect to one mailbox at a time. POP3 protocol assumes that the current mailbox connection is a unique connection. On the contrary, the IMAP4 protocol allows multiple users to access the mailbox at the same time and provides a mechanism for the customer to perceive the operations performed by other users currently connected to the mailbox.

You can access the MIME part and partial part of a message. Almost all Internet mails are transmitted in MIME format. MIME allows a message to contain a tree structure. The leaf nodes of this tree structure are single content types, and not leaf nodes are combinations of multiple types. The IMAP4 protocol allows the client to obtain any independent MIME parts and part or whole of the information. These mechanisms allow users to browse the message content without downloading the attachment or simultaneously obtain the content.
 
Message status information can be retained on the server. By using the identifier defined in the IMAP4 protocol, the client can track the message status, such as whether the email is read, replied, or deleted. These identifiers are stored on the server. Therefore, multiple users can access a mailbox at different times to perceive the operations performed by other users.

You can access multiple mailboxes on the server. The IMAP4 client can be created, renamed, or deleted on the server. The mailbox is usually displayed as a folder ). Supports multiple mailboxes and allows the server to provide access to shared and public folders.
Supports server-side search. IMAP4 provides a mechanism for customers to require the server to search for information that meets multiple criteria. In this mechanism, the client does not need to download all information in the mailbox to complete the search.

Supports a well-defined Scaling Mechanism. Drawing on the early Internet Protocol experience, IMAP's extension defines a clear mechanism. Many extensions to original protocols have been proposed and widely used. Whether POP3 or IMAP4 is used to obtain messages, the client uses the SMTP protocol to send messages. The email client may be a POP client or IMAP client, but SMTP is used.
Most mail program Directory Services also use LDAP.

Unlike most old Internet protocols, IMAP4 is designed to support encryption registration. The plaintext transmission password is also supported in IMAP4. Because the use of the encryption mechanism requires the consistency between the client and the server, the use of the plaintext password is in some clients and server types, such as Microsoft Windows client and non-Windows Server ). SSL can also be used to encrypt communication over the IMAP4 protocol. by transmitting the IMAP4 communication over the SSL protocol through port 993 or declaring "" STARTTLS "when the IMAP4 thread is created ".

IMAP4 uses port 143 to work on TCP/IP connections.