Charles Lindsey writes:
Therefore, I would suggest using something based on the MIME
parameters, such as
Annotations: classification=top_secret;
archived-at="http://foo.example/123456";;
x-spamassassin-score=5
Note that this scheme is fundamentally incompatible with IMAP. In IMAP,
message headers are invariant. Once a client has downloaded a
particular field, it can cache that forever, so that field can never
change. (Search for msg-att-static in the IMAP RFC.)
You probably don't want any mail system extension to be fundamentally
incompatible with IMAP...
Arnt