The CheckMailbox method requests that the server create a
checkpoint of the currently selected mailbox, and updates the current
number of new, unread messages available to the client.
When the client requests a checkpoint, the server may perform
implementation-dependent housekeeping for that mailbox, such updating
the mailbox on disk with the current state of the mailbox in memory.
On some systems this command has no effect other than to update the
client with the current number of messages in the mailbox.
This function actually sends two IMAP commands. The first is the
CHECK command, followed by the NOOP command to poll for any new
messages that have arrived. In addition to polling the server for new
messages, this command can also be used to ensure the idle timer on
the server does not expire and force a disconnect from the