Somewhere in my version of Thunderbird, there is an old adress of one of my correspondant which is recorded This adress is no longer valid and I have deleted it from my adress book

If I had a dollar for everytime I have read that I would be a millionaire

Nonetheless, when I start to write my correspondant's name, this adress keeps being proposed among the first options for the automatic completion of the adress How can I delete this wrong adress from the hidden part where Thunderbird has stored it?

There is at least two address books and my guess is the address is coming from the collected addresses book. This is where outgoing mail addresses are saved when they are not in your address book collection. Generally this is the first address book entry folk have and latter the individual gets added to the main address book, but the original automated save remains to haunt you years later.

Thanks for this first answer I have a french version of Thunderbird When I go in the address books area, I see "Adresses personnelles" and "Adresses collectées" which I could translate respectively as "personnal addresses" and "collected addresses" I have searched the "collected addresses" for the wrong address in the hope to delete it from this area but it does not appear there. I have also search the "Tous les carnets d'adresses" ("all addresses books") but with no better success. I am afraid that the issue is deeper than that Is there another place where Thunderbird stores collected addresses ? If so, how can I access it to destroy the outdated address ?

Do you use the CardBook add-on? Which is your OS? If you are a Mac user the undesired address might be stored in the "Mac OS X Address Book" aka Apple's "Contacts"....