"The message could not be sent because the connection to Outgoing server (SMTP) smtp.comcast.net was lost in the middle of the transaction.Try again."

Recently I have been unable to send email from Thunderbird although I can still receive email in Thunderbird. I get the following error message: "The message could not be sent because the connection to Outgoing server (SMTP) smtp.comcast.net was lost in the middle of the transaction.Try again." However, I can send email when I log into my Comcast email account from a web browser (Firefox). Therefore, when I called Comcast, they insisted the problem in Thunderbird or some other app. I doubt that, however, because a local tech support company took my PC and did the following to troubleshoot the problem: - They tried using an email client other than Thunderbird and still could not send email and got the same error. - They deleted my email account in Thunderbird, uninstalled Thunderbird, and then reinstalled Thunderbird and added my email account but was unable to send email and got the same error message. - They installed Thunderbird on a different PC and added my email account but was unable to send email and got the same error message. - They checked the third-party setting for accessing Comcast email and it was set correctly as Security->Third party access. Here's my configuration. I've also attached screen shot of my Thunderbird settings. • My mail provider: Comcast • ISP: Comcast • Firewall version and antivirus software: Kapersky Total Security version 21.3.10.391 • OS: Windows 10 Home version 22H2 • Thunderbird 115.2.3