<blockquote> I changed the password on the server...but can't find where to change/update the password within Thunderbird. </blockquote> You cannot change passwords using Thunderbird. Thunderbird can only remember passwords, so that you don't have to type it again and again. Try to delete the password Thunderbird has remembered for the troubled account. At the top right of the Thunderbird window, click the menu button ≡ > Settings > Privacy & Security > Saved Passwords > Show Passwords. You'll then be prompted to authenticate again the next time the password is needed.