remove deleted emails

I have no problem with deleting my emails...it's removing them from my computer that is a problem

At the moment, suddenly, I have over 9000 emails with 2335 unread apparently. Some of these emails are not even emails to me or by me. I have thousands of emails that are from folks whom I have never send an email, nor have i received any from these people/companies. Why did they all land on my computer? All this seems to have been precipitated when I signed into gmail...as opposed to my Sympatico mail which I had been using...

What gives????