Removal of email address in "From" field in Mail

Hi,

I have recently changed email addresses. When preparing an email in the "From" field there is drop down that gives you the option of "choose which address to send this message from". I have an old email address that I wish to remove from this dropdown and I new one to add. How do I do that? The old email account has been deleted in Internet Accounts and the new one added but this change does not appear to carry thru to the email page itself.

Thanks