I keep getting an Authentication Required window after deleting an account and making sure that password is not among the saved passwords, there are no traces of the website or the account. How can I fix it?

I have deleted an email account, then I made sure that the saved password and any traces of the account are gone, but every time I launch the program a window pops up with this message: Authentication Required - Mozilla Thunderbird https://ha1012.raiolanetworks.es is requesting your username and password. (and the account I had before deleting it) How can I stop that window from appearing again? Thanks!