I followed up the steps sent by christ1, but none of them worked. I think my problem lies elsewhere. Normally, when I first open Thunderbird and attempt to send email, I'm always asked for my password for the SMTP server. I know what it is and, once I typed it in, the mail was sent. That password is different for the POP server password. I don't remember how I configured it in the Account Settings, because I don't see a place for it. Now, for the last 48 hours, the following happens. That password no longer accepted and I'm repeatedly asked to enter a "new password." As I try to re-enter it or try my POP password, the connection to the SMTP server times out. I went back to my SMTP server settings and noticed that my Authentication method was set to "Password, transmitted insecurely." I don't believe that I'd ever set or changed that setting one way or another. However, when I tried to change that setting to "No authentication," my email was sent with no problem. So, could that be the problem? What was Authentication method be set to normally?