The email metadata idea reminds me of EDIFACT, or at least what it was intended for - a standard electronic format for commercial transactions. It predates the

The email metadata idea reminds me of EDIFACT, or at least what it was intended for - a standard electronic format for commercial transactions. It predates the WWW though, so looks quite 'ugly' by today's standard of using markup language to describe data. However I think it would be a good starting point for coming up with a broadly applicable data schema. [1] https://en.wikipedia.org/wiki/EDIFACT https://en.wikipedia.org/wiki/EDIFACT