Use Smart Addresses
A Smart Address shows a recipient’s name instead of name and email address. This makes it easier to see who you’re emailing.
Mail can show Smart Addresses for people in the Contacts app, in the Previous Recipients list in Mail, and (if you’re connected to network servers—say at work), on available CardDAV, Exchange, or LDAP servers.
If you’re reading a message, move the pointer over a person’s name in an address field to see the Smart Address arrow. If you’re sending a message, the arrow is always shown.
Show Smart Addresses when reading messages: Choose Mail > Preferences, click Viewing, then select Use Smart Addresses.
Show the email address for a Smart Address: Click the arrow in the Smart Address.
Add a Smart Address to Contacts: Click the arrow in the Smart Address, then choose Add to Contacts.
Edit a Smart Address when sending a message: Click the arrow in the Smart Address, then choose Edit Address.
Delete a Smart Address when sending a message: Select it, then press Delete.