Linkedin is a great idea but I don't know if I'd use it as a way to get emails out. Linkedin makes up about 80% of sales in the industry for ones converted from social media. What I'd do instead is I use a tool called dripify where you can upload your search from linkedin sales navigator and it'll allow you to send messages to people directly from linkedin (and if you still wanted to do the email technique, it can collect the email and send stuff out for you). It's more warm coming in as a linkedin message than it is from a cold email. That said, I've done it for a variety of groups: small business owners in my area, realtors, people from the WARN Act. The issue however is that not everyone is active on linkedin and it also depends on the niche you're trying to brand yourself around, some industries have lesser participation. You should check out the web series, identifying the invisible rich because it goes through a lot of great types of people you can reach out to that aren't usually talked about: https://dunham.com/FA/Blog/Posts/identifying-the-invisible-rich