InterIMAP performs stateful bi-directional synchronization between two IMAP4rev1 servers. Compared to the so-called "full" synchronization solutions, InterIMAP 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.