Why doesn't sender names in Mail.app appear as entered in Address Book?

Mail > Window > Previous Recipients > Remove From List

 

When you send mail, even to someone who isn't in your Address Book, it adds them to the Previous Recipients list. If you replied to an email from "emily" she was added to the list. Then when you compose, Mail looks at the list and pulls "emily". If you delete her from the Previous Recipients list, Mail will only be able to find her Address Book entry.

 

That's not quite what the original question was about. The OP is receiving mail from "emily" when the lady in question is Emily Smith in his address book. It is mail that he is receiving that is wrong, not that which he is sending.

I have the same problem. I have Tom Smith in my address book and mail from him has always come from "Tom Smith" Just recently it has started coming from "TS"

 

OK, when you first set a mail account in most mail applications, you have to associate a name to your email address during the set-up processes. Then, when you send an email, your mail application pulls both your address and the name used during configuration and sends that information in the header of your mail. The recipient email application reads the header and displays that information for you. So, when you receive a message the name of the Sender is not pulled from your address book but yes from the header of the email, and that is what causes the difference you see.

I don't know how to make Mail always read the name of the contact associated with Address Book but please, make sure that in preferences you have the option 'Use Smart Addresses' selected.

 

Maybe not the answer to the original question, but this is super helpful for getting rid of those annoying old email addresses when Mail autocompletes your addressees. Thanks!