Why does the display name in older messages change if I update my address book for that E-mail address?

Question

I have recently installed Thunderbird 24.5.0 after upgrading a WinXP machine to Win7. I have discovered a strange problem with older mail that was imported from Outlook Express 6.
The pastor of my church uses a generic E-mail address <[email protected]>. This address belongs to the position, not to an individual. We recently had a new pastor come to the church, and I updated my entry for this E-mail address to reflect the new person's name. This is fine for new mail sent since the new person arrived, but Thunderbird has also applied the new name to older mail from the previous pastor. This is very confusing, since the current pastor could not have sent mail from that address prior to her start date.
How can I get Thunderbird to stop changing the Display Name in archival messages that were sent by the previous pastor prior to September 01, 2013? I have not encountered this situation before using Netscape 4.x Mail, Outlook Express 6, and Windows Mail (Vista version).

Answer 1

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&#64;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.