worry about out going emails getting through

I get 80 % of my work through my website and through corresponding with
email.
People email me regarding my work and pricing and I reply..
Now I know many many folks will get my reply and not write back.. that's
just the way we are.
I try to do follow up in about a week to see if they received my response..
and as I write this I realize I should be religious about follow up.
I never liked the return receipt option..

Are there any tests to see how effective our out going emails are ?
Of course I realize if problems exist it's most likely on the other end
filtering too many emails..

Just looking to learn more about out going email reaching there destination

Joel