feature request: caching message arrival time

[Ralph Seichter]

* Daniel Kahn Gillmor:

> I'm working on Autocrypt integration for notmuch right now [...]

Woot! :-)

> I'm happy to explain more about my use case if people are interested
> too.

I'm interested. Right now I frankly don't know what knowing when a
message was first seen by Notmuch might be useful for. That makes it
a bit difficult for me to contemplate your questions.

-Ralph