I am working on some workflow stuff.

So I use Gmail, has really improved my e-mail management/finding, etc. I process and handle about 400-500 e-mails per day.

Wanting to get to the next level.

I am trying to devise a gmail search that would show me e-mails that I
have sent that I have not gotten a response to?

eg. I send you a message, I never got a response - I would like to
have a search that shows all messages I have sent that have no
responses.... this could then be used to follow-up with that person... obviously the e-mails that I got a response have been actioned....

Any ideas?