При регистрации аккаунта в почтовом клиенте выдает постоянную ошибку

I will share a similar experience and it may relate. I set up an account when I already had one with the same domain. I received the same error message. What I discovered was that Thunderbird did NOT set up an SMTP server for this second account, but left it set to use the same one as the other account. This can cause crazy errors, so I encourage you to check this: # click 'account settings' and then click the account name in left sidebar # now, look in lower right for link to SMTP server. Click the 'edit' button and see if it is the email address of a different account. If so, then do this: # back up to prior screen # click the 'outgoing server' link in lower left # on this screen, create a new SMTP server for this new account and set it appropriately # now, return to account setting pane and click the account name again # this time, click the drop-down menu in lower right for outgoing server and set it to be the newly created SMTP server And, despite all this keying, that may not be your problem, but it might be. Let me know. :)