Should we create or register $hasAttachment flag for JMAP/IMAP mapping

[cjnewman]

JMAP has a boolean hasAttachment property. For JMAP/IMAP mapping, there should be an equivalent in IMAP. The present registry model for JMAP/IMAP keywords allows registering a "reserved" keyword (if we want to define it later) or an "IMAP-only" keyword (if we want to define it in JMAP). I'm willing to supply text either way. I have a slight preference for defining an "IMAP-only" keyword in the JMAP mail spec since the definition of hasAttachment is already in the JMAP spec. For completeness, the third option would be to lose the boolean property and make it a 'both' keyword (with the same definition, but a few caveats for the IMAP case, for backwards compatibility).

[neilj]

Registering $HasAttachment was brought up on the IMAPEXT mailing list 6 months ago: https://www.ietf.org/mail-archive/web/imapext/current/msg05852.html – not sure why Jeff never followed through with this?

I think IMAP-only keyword is fine. I strongly think it should be a property on the Email object rather than a keyword in JMAP because that's immutable and mandates implementation, as explained in https://www.ietf.org/mail-archive/web/jmap/current/msg00488.html