Cold calling and cold mailing are both rather sub-par ways to get clients. Ideally you first prove yourself in your niche/market/area so that people have heard of you and then they approach you and not vice versa.
The only appropriate way to get clients vs the cold approach is to warm up by doing some research and crafting a tailor-made offer specifically for the needs of the given potential client.
You take a closer look at their site, store or product and offer the exact thing they are obviously lacking. Something like "I've noticed that your site is slower than 70% of your competitors. I could do x, y, z to improve it drastically."