(Spam) e-mail marketing is effective but it depends on the approach you take, also learn from the ones that end up in your spam inbox too - to know what "not" to do.
Let's say if you go and say " buy our SEO today and receive 50% off for life " - it "might" work but I bet it won't be any way impressive. Instead, your email can look like this:
Hey {website name},
I have just read your article {article title} and it totally rocked. I have learned a lot of new things. However, I happened to find that you have some errors on your website that may be preventing you from ranking better.
Here's a personal video that I made detailing the errors and how to fix them:
{video link} this must be a personal video, not for the mass
Hope it helps it. If I can help in anyway, please let me know.
You are awesome, once again.
{your name}
"
The site owner will feel grateful that you have just helped him for free, and naturally be more open to you. That's when you try to pitch him little by little. Patience is key, build rapport.