If you send 1000 preschoolers to the computer lab and sit them in front of your landing page, you'll get no signups. Sit 10 businesses you've already spoken to on the phone about their problems, businesses your service could save hundreds of thousands of dollars, and all 10 will sign up. Your website's conversion rate is less than 1%: just 10 out of 1010 people signed up, but you actually converted 100% of your prospective customers.

The point is that websites don't have conversion rates, which is why there aren't any useful blog posts listing what conversion rate you should be aiming for. Whether your 25-30% e-mail opt-in rate is good depends on what percentage of the people you sent to that page were in your target audience to start with.

If 100% of them were people you spoke to on the phone that sounded super interested in your service, maybe 25% is bad. If they're just people clicking through a link in a guest post you wrote on some blog, 25% giving you their e-mail is probably excellent.