Fast bidirectional synchronization for QRESYNC-capable IMAP servers

 InterIMAP performs stateful bi-directional synchronization between two
 IMAP4rev1 servers. Compared to alternatives such as OfflineIMAP, InterIMAP
 trades flexibility and IMAPd compatibility for performance; it is both *much*
 faster and parsimonious in network traffic.
 .
 Stateful synchronization is made possible by the QRESYNC extension from
 [RFC7162]; for convenience reasons servers must also support LIST-EXTENDED
 [RFC5258], LIST-STATUS [RFC5819] and UIDPLUS [RFC4315].
 .
 Furthermore, while InterIMAP can work with servers lacking support for
 LITERAL+ [RFC2088] and MULTIAPPEND [RFC3502], these extensions greatly
 improve performance by reducing the number of required round trips and it
 thus strongly recommended to use a server supporting these.
 .
 InterIMAP supports the COMPRESS=DEFLATE extension from [RFC4978]. It is
 enabled by default on remote servers advertising it in order to reduce network
 traffic, especially for long-lived connections.