Be patient. and do NOT repeat sending too the same reciepants..
* Be sure the 'FROM' email addy is not a freebie like yahoo.. make it a professional/website email address if possible.
* power in #'s.. how many emails have you sent? I generally send over 250+ per domain name I'm marketing.
* phone contact is always a great way to cut too the chase and get too the decision maker..
Goodluck!