Tony Finch wrote:
On Mon, 19 May 2008, Alexey Melnikov wrote:
Regarding metadata transfer: it might be handy. I was thinking about an SMTP
extension for passing IMAP flags from sender to recipient, for example I can
annotate a message with flags using Thunderbird [something I can do already],
then forward the annotated message [something I can't].
The message envelope is lost at final delivery time, so MUA-to-MUA data
transfer has to be done via the message header.
I was thinking that my LMTP server can also support this extension and
will set IMAP flags on delivery.
(This is why there are
different mechanisms for DSNs and MDNs. DSN information is for consumption
by MTAs so it's in the envelope, and MDN information is for consumption by
MUAs so it's in the header.) The IMAP server is a very borderline case
between MTA and MUA so it might not be immediately clear that your idea is
wrong. However you might want to forward a message as an attachment with
IMAP flags, in which case there's no envelope in which to stash them.
Yes, a way to encode metadata in headers would be needed as well.