If you delete an email from your trash folder is there a history somewhere to retreive it?

No! there's no way to retrive it once it's deleted from the trash folder. A bit of advice. DO NOT EVER delete files from that folder. That way you can't delete something by mistake. Yahoo empties that folder (and the Bulk Mail) folder periodically, and those emails take up none of your allowable space. In fact I would check those folders periodically to make sure there isn't something there you don't want deleted.