I have been using Thunderbird to send and received emails for months. Suddenly, I cannot sed emails, but still am receiving emails. I spoke to exhaustion with my email provider's support. They had me try a different IMAP server, messed with settings, and still nothing worked. I am able to send mail via webmail. I attmepted using Mailbird, but am having the same issue as thunderbird. I am wondering if there is some kind of thing blocked with an antivisu program or something? I am using Malwarebytes. I get the error message attached. WHat is blacked out is my domain name. I also get the same message when I attempt the email provider's alternative server. WIth Mailbird, it closes the email as if it sent, but i look in my sent inbox and see it as "pending."