Hi and welcome.
I may be misreading your post, but I think you might mean that when composing an email, even though a contract is deleted, the email address still appears as an option???
The way to sort this out is to Open Mail > go to top menu and select Window > from drop down, choose "Previous Recipients".
This will bring up a list of everyone who has ever emailed you. Look down the list till you find the name you want to delete, Click to Highlight it and select "Remove from List".
This is not only helpful in deleting email addresses of people who have left your circle of friends or passed on; but also allows to delete an obsolete email from someone who has changed their email address so that it doesn't appear as an option. Moreover, you can correct any mistakes in an email address.
I don't know if this is what you meant. Please advise.
Ian