I changed my name in iCloud a while ago, and then reverted that change. iCloud.com, the iCloud System Preference pane, and the info that appears in the Internet Accounts entry for the iCloud account are all correct. In Mail.app, it keeps sending emails as the previous name.
In ~/Library/Mail/V2/MailData/Accounts.plist it shows the old name in Root -> MailAccounts -> Item 3 -> FullUserName, as well as both the EmailAlias entries. I can change these to the correct name in the plist and start Mail.app again, and it will revert these values back again.
I can't find anywhere where my previous name is specified.
Best Answer
From http://kb.mit.edu/confluence/display/mitcontrib/Apple+Mail+shows+incorrect+name+for+email+address: