associating a property with a subpart of a message

[Daniel Kahn Gillmor <dkg@fifthhorseman.net>]

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hey folks--

I have some message properties i'd like to cache in notmuch that
strictly apply to specific subparts of the message.  (e.g. session keys
for an encrypted part, signature verification status of a signed part)

let's assume that for any given copy of a message, we have a reliable
"address" scheme for a part (e.g. "1.2.1.1").

However, this becomes confusing with multiple copies of a given message.
It's possible that one copy of the message has one MIME structure, but
mangling (by MTAs, mailing lists, etc) result in a different MIME
structure in another copy.

For cryptographic properties, it might be nice to associate a subpart
with a particular cryptographic digest of the subpart itself.

Alternately, from a filesystem perspective, maybe it would be better to
label the subpart based on the underlying physical file, and the
subpart's "address".

Are there other options?

If you wanted to associate a message property with a subpart of a given
message in a way that was reliable, especially in this new era of
multiple copies of a message, how would you do it?

         --dkg

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