You're saying that you mailed them once; you didn't get a reply; you mailed them again; you still didn't get a reply; and now you a thinking of contacting them a third time?
And these are people who have never previously contacted you, or who have expressed an interest in purchasing whatever service you are offering?
The conclusion seems inescapable: they are not interested. So, why waste your time with them?
Contacting one or two people at a time, and continuing to press them even though you get no response, doesn't seem like a very efficient form of marketing.