Changed my last name on iCloud, but email won't recognize it. Please help...

Changed my last name (marriage) everywhere I can think of; the only place not allowing me to is in the email app on my MacBook. So, I logged into email through iCloud, made the change there, confirmed the change, and saved it. After logging off, rebooting, and trying few other things, eMail still will not change my last name. The account info is locked in gray, and the settings aren't 'editable.' Please advise on how to update that. Sending emails that are signed with my new last name, but appear in the 'from' line with my maiden name is confusing, especially to new clients, etc. Thank you!!

The new Mrs. Moore