Retrieves information about messages specified by the MessageSet property.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
This method retrieves information for the messages specified by the MessageSet property. This includes information about the message envelope as well as message structure. Every time a message envelope is retrieved, a MessageInfo event is fired, and message envelope information is stored in properties such as: MessageSubject, MessageFrom, MessageRecipients, etc. If the message is a multipart message, one or more MessagePart events are fired before the MessageInfo event - one for each message part.