People write all sorts of names in their address books. Sometimes it's just first name, sometimes it echoes the email address, sometimes it is a nickname. But the email address is always the same.

So when replying, if the email address exists in our Address Book, Claws-Mail should have the option (and ability) to replace the displayed name with what exists in the user's Address Book.

For example, an email received is:
 From: "Fortin, Peter (PMP, OVG, LPA)" <pete@example.com>
 CC: "'Friends > Nana'" <nana@example.com>, joe@example.com

If the email addresses exist in the address book as:
 Peter Fortin <pete@example.com>
 Nana Smithers <nana@example.com>
 Joe Mullock <joe@example.com>

Then, when replying-all to the message, it should look so:
 To: Peter Fortin <pete@example.com>
 CC: Nana Smithers <nana@example.com>
 CC: Joe Mullock <joe@example.com>

Will make things very clean IMHO.