"By May of 2015 I had sent over 30,000 sales and marketing emails so I knew how to get high response rates" It's clear that the author meant he had experience

"By May of 2015 I had sent over 30,000 sales and marketing emails so I knew how to get high response rates" It's clear that the author meant he had experience with sending mail, not that he sent 30k mails about THIS product.