Yesterday 8/15/15 Thunderbird performed an automatic update when I opened it. Since then we can't send email from my wife's account, a+++++++@hughes.net. I tried sending from other accounts and the system worked OK. I checked the settings as suggested by the error message, and all seems ok. An error occurred while sending mail. The mail server responded: 5.1.8 [F18] Sender antiques@hughes.net mailbox is unavailable.. Please verify that your email address is correct in your account settings and try again This is the first problem we've experienced since we started using Thunderbird a couple of years ago. Thanks. Bill Darbyshire edited emails from public and spambots.