This feature would be analogous to the current "Display sender using address book" preference. When composing a reply, if the To address is in your address book, Claws would format it as it does in the message list rather than exactly as in the From (or Reply-To) header in the original email. 

e.g.: 

original email:
From: "SMITH, John" <John.Smith@EXAMPLE>COM>

address book:
Display Name: John Smith
Email Address: john.smith@example.com

message list when "Display sender using address book" preference is not set:
From: SMITH, John

message list when "Display sender using address book" preference is set:
From: John Smith

to header in compose window with new preference set:
To: John Smith <john.smith@example.com>

Hope this request is clear - it would seem that most of the code is already there for the current "Display sender using address book" feature.