When Thunderbird's e-mail address completion offers you an address you don't find in your address book

I discovered the other day that Thunderbird was offering me two addresses for an old friend I hadn't e-mailed in a long time. I checked them both and found out that one of them was defunct.

So I went to my address book and tried to delete the offending address. But I only found one entry for her, listed with the address that worked. I'd assumed there were two entries for her in the address book.

There weren't. Instead, the bad address was in the Additional Email field....which isn't listed with the person's name in the table of addresses in the address book. You have to display the full details of the entry to see it.

I use the Portable Thunderbird version of the app. I'm very happy with it. I keep files on two different systems and sync them with each other daily. This way I have backups and easy access to my files in two locations.