comcast email send failure

I use Thunderbird 115.7.0 with Windows 7. I have two Comcast email accounts. Both can receive email; neither can send email. My gmail account on Thunderbird works fine. When I try to send, I receive the message, "Sending of the message failed. Unable to authenticate to Outgoing server (SMTP) smtp.comcast.net. Please check the password and verify the 'Authentication method' in 'Account Settings | Outgoing server (SMTP)'." I have checked Thunderbird's saved passwords and the password I enter is correct. Settings are: Server Type = Imap; Server Name = imap.comcast.net; Port 993; Connection Security SSL/TLS; Authentication method = normal password; Outgoing Server = Comcast smtp.comcast.net (default); Port = 465; SSL/TLS; Normal Password. Comcast customer service has been of no help. They have twice promised to call back in an hour and I never heard from them. I have tried changing authentication methods, changed the password, had Thunderbird create a new account, moved my records to it, and removed the old account -- all to no avail. I don't know what caused this problem about a month ago and have no idea how to fix it. Any ideas would be appreciated.