Not able to send email via Thunderbird but receive email easily

This month I downloaded the current version of Tbird on a new computer running windows 11. Tbird receives all my email but can not send mail. I have an old computer running on windows 7 which has Tbird that was loaded at least 5 years ago. It receives and sends email without problems. The two versions of Tbird are using the same SMTP settings: server: mail.twc.com Port: 587. My email account for Tbird is xxxx@triad.rr.com I also have a gmail account which receives and sends on both computers without problems. My gmail account is xxxx@gmail.com. Both computers run through the same internet network.