Internet Message Access Protocol  

The Internet Message Access Protocol (IMAP) is an application protocol which is used to access a user's email messages which are stored on a mail server. However, unlike the Post Office Protocol (POP) where messages are downloaded and processed on the local system, the messages on an IMAP server are retained on the server and processed remotely. This is ideal for users who need access to a centralized store of messages or have limited bandwidth. The SocketTools IMAP control implements the current standard for this protocol, and provides methods to retrieve messages, create and manage mailboxes, and search for specific messages based on some user-defined search criteria.

The following properties, methods and events are available for use by your application:

Initialize the control and validate the runtime license key for the current process. This method is normally not used if the control is placed on a form in languages such as Visual Basic. However, if the control is being created dynamically using a function similar to CreateObject, then the application must call this method to initialize the component before setting any properties or calling any other methods in the control.

Establish a connection to the IMAP server. Once the connection has been established, the other methods in the control may be used to access the messages on the server.

Disconnect from the server and release any resources that have been allocated for the client session. After this method is called, the client session is no longer valid.

Unload the Windows Sockets library and release any resources that have been allocated for the current process. This is the last method call that the application should make prior to terminating. This is only necessary if the application has previously called the Initialize method.

Managing Mailboxes

One of the primary differences between the IMAP and POP3 protocol is that IMAP is designed to manage messages on the mail server, rather than downloading all of the messages and storing them on the local system. To support this, IMAP allows the client to maintain multiple mailboxes on the server, which are similar in concept to message folders used by mail client software. A mailbox can contain messages, and in some cases a mailbox can contain other mailboxes, forming a hierarchy of mailboxes and messages, similar to directories and files in a filesystem. A special mailbox named INBOX contains new messages for the user, and additional mailboxes can be created, renamed and deleted as needed. Here are the most important methods for managing mailboxes:

Check the mailbox for any new messages which may have arrived. Because messages are managed on the server, it is possible for new mail to arrive during the client session.

Create a new mailbox on the server with the specified name.

Delete a mailbox from the server. Most servers will only permit a mailbox to be deleted if it does not contain any mailboxes itself. Unlike deleting a message, which can be undeleted, deleting a mailbox is permanent.

Once the session has been established and authenticated, a mailbox should be selected. This enables the client to manage the messages in that mailbox. This method selects the specified mailbox in read-only mode so that messages can be read, but not modified. To select the mailbox in read-write mode, use the SelectMailbox method.

Renames an existing mailbox. One of the interesting uses of this method is the ability to rename the special INBOX mailbox. Instead of actually renaming it, it moves all of the messages to the new mailbox and empties the INBOX.

Once the session has been established and authenticated, a mailbox should be selected. Selecting a mailbox enables the client to manage the messages in that mailbox. This method selects the specified mailbox in read-write mode so that changes can be made to the mailbox.

This method unselects the currently selected mailbox, and allows the caller to specify if messages marked for deletion should be expunged (removed) from the mailbox or reset back to an undeleted state.

Managing Messages

There are methods in the IMAP control for managing messages which enables the application to create, delete and move messages. To use these methods, a mailbox must be selected, either by setting the MailboxName property or calling the SelectMailbox method. Methods which modify the mailbox require that it be opened in read-write mode. Messages are identified by a number, starting with one for the first message in the mailbox.

Copy a message to a specific mailbox.

Mark the specified message for deletion. Unlike the POP3 protocol, when a message is deleted on an IMAP server it can still be accessed. The message will not actually be removed from the mailbox unless the mailbox is expunged, unselected or the client disconnects from the server.

Remove the deletion flag from the specified message.

Viewing Messages

One of the more powerful features of the IMAP protocol is the ability to precisely select what kinds of message data you wish to retrieve from the server. It is possible to retrieve only specific headers, or specific sections of a multipart message. Because IMAP understands MIME formatted messages, it is possible to only retrieve the textual portion of a message without having to download any attachments that may have come with it.

This method returns the value for a specified header field in the message. Using this method, it is not necessary to download and parse the message header.

This method retrieves the complete headers for the specified message and stores it in a string or byte array provided by the caller.

This method retrieves the specified message and stores it in a string or byte array provided by the caller; you can specify the type of message data that you want, a specific part of a multipart message and the amount of data that you want. For example, it is possible to request that only the first 1500 bytes of the body of the 3rd part of a multipart message should be returned.

This method is a lower level method which opens a message for reading from the server. The application would then call Read to read the contents of the message, followed by CloseMessage when all the message data has been read. Also see the GetMessage method, which will return the contents of a message into a string or byte array.

Downloading Messages

In some cases, it may be preferable to download a complete message from the server to the local system. This can be easily done with a single method call.

This method downloads a complete message and stores it as a text file on the local system.