Of course it does. It looks for a match between the sender's email address and a Contact in your address book. You've edited the Display Name for this account so it gets applied to any message with that email address if that's how your Address Book is configured.

In the Contact card for this address, you can tell it whether or not to use the "real" email address within the message, or the Display Name from your Address Book. Telling it to use the name found in the message might resolve this, but it depends on how the sender has formatted it. If he includes his name then Thunderbird should be able to resolve it, and you just add both configurations to your Address Book as two separate Contacts, rather than modifying the existing entry.

However, in this situation you're using the same email address for two distinct people, so Thunderbird may not be able to know who sent the old messages. If both have sent using "rector@stpeterscobourg.org" without any personalization then Thunderbird won't be able to differentiate between them.

I have to say that I haven't recently tried using different display names with the same email address, so I don't know for sure if TB can use the display name constructively. If there's nothing in the old messages to tell you which sender wrote them, then TB can't do anything about it.

Zenos - Thanks for your reply. It *partially* addresses my problem, in that making the changes that you recommended to the duplicate Address Book entries forces each person's name to appear correctly in the Index view of my messages. The body of each message, however, still shows the newer person's name in all messages sent by the common E-mail address, including those sent by her predecessor before she ever arrived.

I have given up on Thunderbird, and reluctantly gone back to using Outlook.