E-mail indexing

I’m now using swish++ to index and search my mail. It’s really handy,
particularly with the patched nnir.el and
doc/examples/email_indexing/Email-Indexing-Mini-Howto.txt . I’ve set
it up to index my misc mail and my planner mail, as those are the
things I search rather often. Should set it up to incrementally index
things before I go to sleep.