If you subscribe to Redtail's Email Archiving service, at some point you're probably going to have a situation where one of your clients changes their email address. Then, the question will arise of whether you need to keep their old email address in Redtail in order for older archived emails to remain in their record. The answer is yes.
In order to preserve the email address within your database (while hiding it from view), you can go to the record's Contact Card, click the old email address' Actions menu, and select "Archive Email":
This will hide the address but preserve archived correspondence.