Thunderbird. I have been using it successfully for 14 years. Now I can no longer send email. I have 6 email accounts (gmail, outlook, yahoo, att, etc.) and all receive email. Outgoing mail and saving a draft time out and fail. The yahoo account asks for my password, but does not accept it. (It is correct because I can access that account without using the thunderbird client. What is a secure mail key? I seem to have one at least for one of my accounts, but I don't know what do to with it.