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My site has 100+ unique articles and all are having 400+ words. I was getting 3K visits to this till yesterday. I haven't done any link building BH or WH to the site recently only just few bookmarks. I also personally believe that the redirect itself should not be the reason but can't find any valid reason to for this deindexing.

I think this is an interesting topic to discuss though I'm looking for answers too.

One of my well performing domain deindexed by Google today.

Reason: Redirect from a 9 year old Deindexed domain (Must be penalysed)

I believe this is done by one of my competitor.

What you people suggest me to do now?

Don't you think if this is the way Google treat the redirects after Penguin anybody can use this technique to harm their competitors?