The account name is not really a server setting. It's a name used to identify each account in Thunderbird. That way you can have accounts with the same server name, and be able to identify each one in Thunderbird. From what I understand, Thunderbird is not letting you access the settings, because there are 2 or more accounts with the same account name, so we need to change the account name outside of the account settings window. There is a way to do that. You need to use the Config Editor. # Go to '''Tools > Options > Advanced > General''', and click on '''Config Editor'''. # In the Config Editor search field, type '''mail.server.server''' # You'll see a bunch of preferences in bold. There is a separate server number for each account. The preferences that end with ''.name'' are the ones with the account name. Look for any ''.name'' preferences that have the same value. (If an account doesn't have a ''.name'' preference, I think the hostname is used.) # Double-click on a preference to change the value. So if you see something like ''mail.server.server1.name Gmail'' ''mail.server.server3.name Gmail'' Double-click on one of them, and change the value to ''Gmail-2'' That should at least prevent the error from popping up, so you can make more permanent changes in the Account Settings window.