Hi
Well really, it's down to you!
What email client do you use?
If Livemail and Outlook Express ... Tools/Accounts .. look for the OLD account name with the entries in it for the old address and delete it. Sounds like you still have the old email settings active in the Mail Accounts.
And ... Keep your new email address OUT of those Yahoo or Hotmail circular emails some people (the un-informed ones) like to send around .. They harvest addresses and will end up on a spam list)
And .. Keep off of websites .. apart from buying/selling sites.