Depends on what your audience is. I have almost reached the conclusion that cold emails don't work for developer products. I have hand written 100+ emails to super relevant people with a few different messaging/subject line etc. While the open rate is high (~70%), the response rate is in single digit percentage. These stats are great for automated system but I expect much better for individually curated emails for a curated list of recipients. It's a big time & energy sink.

Maybe I need to start following up on emails a little more. But I typically don't feel like spamming people if they haven't responded to my initial email.

On the other hand blogs seem to provide most bang for your buck.