Here is my basic rule
Now we've got that out of the way we can add a little finess
* think about putting techy terms in ways that are meaningful to the recipient
* add a topic keyword so it can be easily filtered like on the old discussion group days
* what kind of mail is it, request for info, something that requires action etc.
So a typical subject line might look like..
Info Req - BigLabs Project - network data load
You can then get even smarter by sealing some tricks from bloggers and clickbait by creating provocative headlines to encourage people to open your mail. Check out huffington post for some examples.