IETF RFC 8514 PDF

This document adds a new capability called "SAVEDATE" to the Internet Message Access Protocol (IMAP). It defines a new IMAP message attribute called "save date" that, unlike the existing "internal date" attribute, always indicates the moment at which the message was saved in its current mailbox. The SAVEDATE capability extends the FETCH command with the means to retrieve the save date attribute and extends the SEARCH command to allow using the save date attribute in searching criteria.