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Thallu - IMAP Server Details


IMAP Server Description

The IMAP server (Internet the Message the Access Protocol) Protocol is a Application Layer for access to e-mail.

  • It is based on the TCP transport protocol and uses port 143.Also IMAP's uses port 993. IMAP server only works with messages and does not require any packets with special headers.
  • IMAP server offers the user ample opportunities to work with mailboxes located on the mail server. A mail program using this protocol gains access to the correspondence repository on the server as if this correspondence is located on the recipient's computer. Emails can be manipulated from the computer of the user without constantly sending from the server and back the full contents of the letters.
  • SMTP is usually used to send letters and since its own IMAP server sending command. so it called APPEND then it does not contain a mechanism for transferring service information.
  • For mailbox names with characters outside the ASCII range and modified version of the UTF-7 encoding is used.
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    Purpose of developing the IMAP server protocol

    IMAP server is an alternative to POP with basic sending capabilities.The first version of the POP protocol had several shortcomings and the most serious of them was the lack of capacity to control the movement and storage of messages on the server. In POP, messages are downloaded from the mail server all at once after which they are deleted from the server, that is, there is no way to select messages to receive.

  • In order to solve the problems associated with this feature POP in 1986, Mark Crispin, then at Stanford University and has created a new protocol to get mail from a server.
  • The new protocol offered users with the ability to receive e-mail in various places from one mailbox. The user is given the opportunity to manage messages in his mailbox and additional functions for servicing mailboxes on the server.
  • Subsequently the POP protocol was finalized; in POP3. it is possible to receive selected messages from the server and leave selected messages on the server. In the latest versions between IMAP and POP and the main difference for the user is that IMAP4 can access letters in different mail folders on the server and move letters between them, while POP3 addresses messages on the server by numbers in the linear list.
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    IMAP server protocol Versions

    IMAP in 1986 implemented on DEC and no specification.IMAP2 implemented in 1987 then it described in 1988 in RFC 1064, finalized in 1990.IMAP3 1991 RFC 1203.IMAP2bis, the specification exists only in the draft version of 1993, plus RFC 2061 describes the differences between IMAP4 and IMAP2bis.IMAP4 1994 RFC 1730.IMAP4rev1 1996 RFC 2060, 2003 RFC 3501.

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    Advantages over POP3

    When using POP3, the client connects to the server only for the period of time necessary to download new messages. When using IMAP, the connection does not break while the user interface is active, and messages are downloaded only at the request of the client. This allows you to reduce the response time for users in whose mailboxes there are many messages of large volume.

    The POP protocol requires the current client to be the only one connected to the mailbox. IMAP allows multiple clients to simultaneously access the mailbox and provides the client with the ability to track changes made by other clients connected at the same time.

    Thanks to the flag system defined in IMAP4, the client can monitor the status of the message. flag data is saved on the server.

    IMAP4 clients can create, rename, and delete mailboxes and move messages between mailboxes. In addition, you can use the IMAP4 Access Control List Extension to manage mailbox access rights.messages are searched on the server side.IMAP4 has an clear extension mechanism.

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    IMAP messages and their attributes

    IMAP only works with messages and does not want any packages with special headers. Each message has several attributes associated with it. These IMAP's attributes can be defined individually or in conjunction with other attributes.

    IMAP UID

  • Each message is assigned a 32-bit code and when used together with a unique identifier and forms a 64-bit sequence that guarantees unambiguous identification of the message in the Mailbox. The later a message arrives, the greater is IMAP's UID.
  • The UID is associated with the mailbox and is sent as a response uidvalidity code in the mailbox selection phase. If the UID from the previous session can't be used for some reason then the UID must be incremented in IMAP.
  • The UID of the message should not be changed within the session; it should not be changed from session to session. if it is not possible to store the message UID in a subsequent session then each subsequent session should have a new unique identifier code, which should be greater than any UID used previously in IMAP.
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    Message serial number in IMAP

    In IMAP, serial number of the message in the mailbox starts with 1. Each message starting from the second and has a serial number exactly 1 greater than the previous one.

  • During the session it is permissible to modify the message Sequence Number. For example, when a message is removed from a mailbox then the numbers of all subsequent messages change.
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    Message Flags in IMAP

    This IMAP's attribute is a list of zero or more named tokens associated with this message. The flag is set by adding it to this list and zeroed by deleting it. There are two types of flags in IMAP 4.1. The flag may be permanent or valid only for the duration of this Session.

    A system flag is a flag whose name is defined in the protocol specification. All system flags begin with a character.

    The following system flags are currently defined in IMAP:

  • seen - message read
  • answered - a reply was sent to the message
  • flagged - the message is marked as "important"
  • deleted - message marked as deleted
  • draft - message marked as draft
  • recent - recent message
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    Internal date and time of the message on the IMAP server

    In IMAP, Time and date of receipt of the message. In the case of message delivery via SMTP and the date and time of delivery to the final recipient. For messages delivered by the copy command and the internal date and time of the sender of the message. When utilizing a command append then the date and time specified by the command parameters.

    Other attributes in IMAP

  • message size - the number of octets in the message.
  • message envelope structure.
  • message body structure
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    Client-server interaction in IMAP

    An IMAP 4.1 connection involves establishing a connection between a client and a server. The client sends commands to the IMAP server and the server sends data and notifications about the status of the request to the server. All messages, both client and server, are in the form of lines ending with a special sequence.

  • Any policy with the client's team. Any client command starts with a prefix identifier Called a label in IMAP. The client generates its own label.
  • There are two cases where the line sent by the client does not constitute a complete command in IMAP. In the first, the command argument is supplied with code that determines the number of octets per line. In the second, the command arguments require a response from the server. In both cases of IMAP server sends a command continuation request starting with a character.
  • The client must complete sending one command before sending another.Also in IMAP protocol receiver of the server reads the line of the command that came from the client and parses it selects the parameters, and transfers data to the server. At the end of the command server sends a response in IMAP.
  • Data transmitted by the server to the client, as well as status responses that don't show completion of the command in IMAP and have a prefix and are called untagged responses. Data can be sent by the IMAP server in response to a client command or on its own initiative. The data format does not depend on the reason for sending.
  • A response shows a successful / unsuccessful operation. It uses the same label as the client command that started the procedure in IMAP. Thus, if more than one command is being executed, the server label shows the command that caused the response. There are three types of server termination response: ok(successful), no(failure), bad(protocol error).
  • The protocol receiver of the IMAP 4.1 client reads the response line from the server and takes action in accordance with the first character * or +.
  • The client should be ready to accept any server response at any time. IMAP Server data should be recorded so that the client can use it directly without sending clarifying requests to the server.
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    IMAP Server Status

    An IMAP 4.1 server is in one of four states.Most commands can only be used in certain states.In a non-authenticated state, the client must provide a name and password before most commands are available to it. The transition to this state is made when a connection is established without preliminary authentication in IMAP.

  • In the Authentication state, the client is identified and must select a IMAP's mailbox, after which commands for working with messages will become available to him. The transition to this state occurs when a connection is established with preliminary authentication, when all the necessary identification data is issued, or when the mailbox is mistakenly selected in IMAP.
  • The system enters the selection state when the mailbox has been successfully selected.The system enters the exit state when the connection is interrupted as a result of a client request or as a result of an independent IMAP server solution.
  • IMAP Connection without preauthentication.
  • Preauthentication Connection.
  • Connection rejected.
  • Successful completion of a team LOGIN or AUTHENTICATE in IMAP.
  • Successful completion of a team SELECT or EXAMINE.
  • Command execution CLOSEor unsuccessful command SELECT or EXAMINE.
  • Executing a command LOGOUT, shutting down a server, or disconnecting.
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    IMAP server Commands

    LOGIN - Allows the client to use the user ID and password in plain text when registering with the IMAP server. This is not the best method, but sometimes this is the only way to connect to the server.

  • AUTHENTICATE - Allows the client to use alternative authentication methods when registering with the IMAP server. Individual user authentication is optional and is not supported by all IMAP servers.If all attempts to determine the authentication method have failed, then the client attempts to register with the server through the command LOGIN.
  • CLOSE - Closes the mailbox. When a mailbox is closed using this command, messages marked with a flag DELETED are deleted from it in IMAP. It has no parameters.
  • LOGOUT - Then IMAP Ends a session for the current user ID.
  • CREATE - Creates a new mailbox. The name and location of new mailboxes are determined in accordance with the general specifications of the IMAP server. DELETE - Applies to mailboxes. Upon receipt of this command, the IMAP server will try to delete the mailbox with the name specified as the argument to the command. Messages are deleted along with mailboxes and cannot be restored.
  • RENAME - Changes the mailbox name. This command has two parameters - the name of the mailbox that you want to rename, and the new name of the IMAP's mailbox.SUBSCRIBE- Adds a mailbox to the list of active client mailboxes. This command uses only one parameter - the name of the mailbox to be added to the list. A mailbox does not have to exist in order to be added to the list of active mailboxes - this allows you to add mailboxes that have not yet been created to the list of active mailboxes, or to delete them if they are empty.
  • UNSUBSCRIBE - Removes mailboxes from the list of active ones. It also uses one parameter - the name of the mailbox and removed from the list of active client mailboxes. However, the mailbox itself is not deleted in IMAP.
  • List - Get a list of all client mailboxes; has two parameters.
  • NOOP - The team does nothing. It can be used to maintain activity during a session so that the session does not terminate on the timer for the wait interval. Server response to the command NOOP should always be positive in IMAP. Since the server often returns the status of the execution of a command in a response, NOOPit can be used as a trigger to periodically query the status of the IMAPserver.
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    Thallu uses IMAP in Roundcube

    We can setup your own mailing server using Roundcube IMAP Email software. Also our service is Unlimited Bulk Mailing Server setup.Also You use IMAP read and replay in warmup process.

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