How to stop unwanted old addresses appearing in "To" field?

When starting a new “send” email I often get addresses automatically appearing in the “To” field that are no longer in use. these are not present in my Contacts list. How do I stop this?

To manually clear a recipient out of the To: line go to “Menu / Settings / Mail / Compose” and click “Show Receipients” as in the below eM Client V9 example. You can then delete whichever ones you like.