Most probably your gmail account has been hacked.

I assume that you sent out mails with that subject.

My advice:

1. Don't use gmail for such subjects.
2. Change your gmail password to a strong one, I will recommend more than 15 characters.
3. You can filter (g)mails on many different criteria eg:
   
   wind turbine
4. If you have to use a free email service, why not use Opera mail?

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