QRESYNC – efficient IMAP synchronization

	QRESYNC has been implemented in tinymail. http://pvanhoof.be/blog/index.php/2007/10/18/qresync-support-in-tinymail
In short, without implementing this extension, synchronization of IMAP needs to fetch all flags for the mailbox to know which flags changed and which message has been deleted (no response will be returned for the given message): that’s how etpanX currently works. I’ll have to implement it in libEtPan! …