I noticed that the 4 search types that are available are:

"is"
"contains"
"beings with"
"ends with".

The first two could probably be negated and be useful, as well,
as in "isn't" and "doesn't contain" (i.e. I might want to search my
inbox for all messages where I'm not explicitly in the To: and Cc:
lists).

The logic to do this would be trivial in incremental terms.

Is it worth filing a bug?

Thanks,

-Philip