I am working on a education portal since last 2 years. The site has working very well before the last 2 penguin updates that is penguin 2.0 and 2.1. My site is completely affected by the penguin 2.0. After that I have removed all the irrelevant back links and resubmit it again. After that my site was working very well. I always got 25k visits on daily basis on my site, but after penguin 2.1 again there is lost of 80% in traffic and ranks. Now I am getting only 3 to 5K visits on daily basis. Now at this time there is not any manual web span is there. I also got the same mail from webmaster regarding this. I do not know now that what to do to get back the actual positions of site. Looking for your suggestion as soon as possible.
To be honest with you, once your site got flagged or slapped by Google, even if you managed to recover, the fact that your site got slapped won't get erased from your domain's history. In other words, it is much easier, faster and more economical to start over rather than fixing your already penalized site.
Move your content to a new domain and start your SEO campaigns from beginning. Be careful of blackhat techniques. Always try to get high quality links from relevant sites.
Pay attention to social media marketing as well.
All the Best!
What Kronomia said is right.
Once your are slapped by any update it is hard to recover from it.
Even of you change the content and remove all spam backlinks still your SERP's will not increase.
Try register a new domain and start your new campaign.
I agree With Kronomia, Better you buy a new domain and start fresh