Nice, would love to be a part of the expert course!

A lot of good advice. But you do need to keep in mind that even though cold email often works very well for many niches. Some are just not present in their email inbox. I could imagine that plumbers would rather just work and not sit in front of their computer. So if you know that the leads/data you have is good then consider if email is the right way to contact them. If you still believe that email is the right way to contact them, then you can star to a/b test your subject line :)

Keep the e-mail short and use personalisation to stand out from the crowd. I usually structure my emails like this: Intro/first liner Offer Case study CTA