IETF RFC 5957 PDF

Introduction

The [SORT] extension to the [IMAP] protocol provides a means for the server-based sorting of messages. It defines a set of sort criteria and the mechanism for determining the sort value of a message for each such ordering.

The [SORT] FROM and TO orderings sort messages lexically on the [IMAP] addr-mailbox of the first address in the message's From and To headers, respectively. This document provides two alternative orderings, DISPLAYFROM and DISPLAYTO, which sort messages based on the first From or To address's [IMAP] addr-name (generally the same as its [RFC5322] display-name), when present.

A server that supports the full [SORT] extension as well as both the DISPLAYFROM and DISPLAYTO sort criteria indicates this by returning "SORT=DISPLAY" in its CAPABILITY response.