Sending SPAM to get SEO clients is only going to work if you know what you are doing with SPAM. Otherwise, one spam report can close your hosting account, suspend your domain, or both.
But the real problem is think about the message you are sending potential clients: "My SEO does not work for my business, but I am sure it will help you to get customers. Please hire me to do your SEO."
If you know how to do SEO, you would not be asking this question. If your SEO is not generating enough customers, then you need to look at your web site and business and try to figure out why.
- Prices too high?
- Web site sucks or is broken?
- Services offered are confusing or worthless?
- Maybe your SEO is generating the wrong kind of traffic?
When I started doing SEO full time with my own business back in 2004 I did start using email. I would visit sites, pick ones with little or no SEO, and send them a message about how I could help them. It was just AWFUL and I almost got reported for spam, but I wrote personal emails each time.
What I later did that worked well is joined a lot of forums and posted messages that helped people, mostly NOT about SEO. I had a good SIG and if people liked what I posted they remembered me. TIP: Don't just go to SEO forums. Go to forums on topics you know or are interested on and where you can impress people with your posts. You will get links to your site and your posts will be advertising your business for years.

Just NEVER post about your SEO business unless someone asks you. Never advertise or spam or it just won't work. Good Luck!