OS: Win 8.1 ISP: Comcast Thunderbird: 45.0 Since the update, I am able to receive email, but not send it. There is no error message. No "sending mail" progress bar. Nothing. The email just remains on the screen after I click "Send." I have checked SMTP settings. No ports appear to have changed from settings prior to the update. I have checked that the correct SMTP servers are being used. I don't store passwords in Thunderbird. It continues to prompt for password to receive email, but does not ask for SMTP password since the update. I have tried turning off Windows Firewall -- no change. I have gmail accounts and domain-based email addresses. All are set up as POP accounts in Thunderbird. This problem occurs across all accounts. I am able to log into webmail for all accounts and send email, so there is nothing wrong with the ISP, or the accounts. I tried to go back to a restore point prior to the update, and I got a message that Thunderbird couldn't load XPCOM--so I undid the restore point. After that, I could once again open Thunderbird, but the situation as described above continues. I don't know what else to check. Any help would be appreciated.