New Problem - Thunderbird Not Able to Send Email on One Account - Get Login to server smtp.comcast.net with username Error

I am running Windows 10 and Mozilla Thunderbird as my email client. I have multiple comcast.net email addresses set up and all have been working fine. Now all of a sudden I am unable to send emails from one of my accounts, always getting the error message - Login to server smtp.comcast.net with username [Edited: "Personal Information"] failed.

I have not changed my comcast email password, and even went into both my comcast email account settings for that id ([Edited: "Personal Information"]) as well as the account settings in Thunderbird - all are set to the same password.

Can you help? I need to send an urgent email out from that email account. Thank you in advance for your help or direction.

Best regards,

David [Edited: "Personal Information"]