Help with "ESMTP server temporarily not available"

I am trying to send email from my Thunderbird account on my HP laptop and receive this error message: "resomta-h2p-554995.sys.comcast.net resomta-h2p-554995.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available."

I recently switched to the AT&T fiber network, and I recently updated my comcast.net email password. I can send and receive email normally from my iPhone, iPad, and directly on the Xfinity mail website. I can receive email via Thunderbird on my HP laptop but I get the error message when sending.

I would love to have this issue resolved. Many thanks.