Have used Thunderbird for some time now with NO problems. Then I received a notice from Comcast (xfinity) that I needed to change my password, so I did. Deleted old password in Thunderbird and added new one. (Yes, I'm sure it is correct, I've put it in numerous times..) Receiving comcast email just fine but when trying to send I get this error message: Sending of username did not succeed. Mail server mail.comcast.net responded: [AUTH] Authentication failed. Thunderbird gives me the option to Retry, Enter New Password or Cancel. I've tried them all. I've deleted and reentered the new password in Thunderbird repeatedly. Comcast says my SMTP port should be 587 or 465 if needed. Was set on 465 but have tried them both. I've tried choosing no authorization for SMTP instead of 'normal password' and receive this error message: An error occurred while sending mail. The mail server responded: 5.1.0 Authentication required. Please verify that your email address is correct in your account settings and try again. No matter what I try, I still am unable to send comcast email via Thunderbird. Please help! Mail provider: Comcast (xfinity) Firewall/Antivirus: Norton security suite (provided by comcast) OS: Windows 7 Home Premium 64-bit Version: Thunderbird 60.0b10