You may be trying to edit an existing contact's email address but when you go to save the contact record you may be getting the message that that email address already exists in your account?
A: Here is the solution to this:
1) Check in your archived contacts and in all likelihood they are there.
2) Unarchive them temporarily.
3) Edit the previously archived record to disable that email address e.g. insert a 1 in front of the email.
4) Archive this disabled contact.
5) You should now be fine to edit the "live" contact record and save the change.
Hint: If you are copy/pasting the email addresses make sure that you DON'T copy any spaces either before or after the actual email address.