<blockquote> I saw an entry here describing the same problem I have, namely entering an SMTP password in Thunderbird. </blockquote> How exactly is that a problem? Because you forgot your password? Or Something else? <blockquote> I am no longer able to send emails. </blockquote> See https://support.mozilla.org/kb/cannot-send-messages Specifically for Yahoo, also see https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo Do you get any error message? <blockquote> I find two (2) different places to make settings and the answers to the Jan 30 entry never once mentioned how to enter the alphanumeric characters to an SMTP server. </blockquote> Thunderbird will prompt you for the SMTP server password when it's needed. You can then tell Thunderbird to remember that password, so that you don't need to enter it again, and again. <blockquote> And does anyone have a block diagram to explain the structure of : 1. a Yahoo app password 2. a Yahoo mail password 3. a Thunderbird password 4. an SMTP password </blockquote> Not sure what block diagram you expect. 1. You're supposed to use OAuth2 authentication for Yahoo. With OAuth2 there is no app password. 2. Your Yahoo account password. Use that to authenticate to your Yahoo account when using Thunderbird. 3. There is no Thunderbird password. Having said that, in Thunderbird you can set up a primary password, which protects any account password(s) you told Thunderbird to remember. See https://support.mozilla.org/kb/protect-your-thunderbird-passwords-primary-password 4. Same as your Yahoo account password. With OAuth authentication you'll be prompted for your account password only once. There is no distinction between a password for the incoming and outgoing server.