Tools/Account Settings, select the account in the left pane, then Account Actions at the bottom of the left pane, Remove Account. You can't remove the default account, so set another account as Default (Account Actions), then Remove the other account.

I am using a French version 30.3.0.6912 There is no Account Settings button in Tools. Eventually I found it : Options / Account Settings / Accounts management / Delete Account

Pieracha said

I am using a French version 30.3.0.6912 There is no Account Settings button in Tools. Eventually I found it : Options / Account Settings / Accounts management / Delete Account

Two things.... You posted from a windows 10 computer, but reply here with a menu location for Linux. You are unlikely to get useful information unless you correctly identify what operating system you are looking for. Especially as the knowledge base is set up to default show you information for the operating system you access it from. So you search using Windows you get information for Windows.

The second thing is you have said you removed the account. That is not removing an identity. Each email address comes with a default identity, which is associated with the email account. But an email address can have many identities which are managed from the account settings pane on the entry for the account above "server settings"

You are apparently happy with the result however, so I will mark your last post as solving the topic.

1. Delete account : Yes, to me the problem is solved. Thanks for your help. 2. New topics? 2.1 I am not aware of using a "menu location for Linux". I reply on the location indicated in the email I received. I quoted the version number I found on my Thunderbird.exe file. Linux was never installed on my computer. 2. 2 I still don't quite understand the difference between "identity" and "account" - I have never used several identities for a single account, however I should be able to find a tutorial about it.

The difference between accounts and identities, in TB usage, is explained here:

http://kb.mozillazine.org/Multiple_identities_per_e-mail_account