The GetHeaders method is used to retrieve the message
headers from the server and copy it into a local buffer. This method
will cause the current thread to block until the article transfer
completes, a timeout occurs or the transfer is canceled. During the
transfer, the OnProgress event will fire periodically,
enabling the application to update any user interface objects such as
a progress bar.
Note that the header data will be from the first part of the
message, not from any additional sections of a multipart message. In
other words, the headers such as From, To, Subject and Date will be
returned in the buffer. To retrieve the headers from a specific
section of a multipart message, you can use the GetMessage
method and specify the imapSectionHeader option.