To send books to the Kindle, Libtro sends an email on your behalf. Google does not allow other apps to use your regular account password, and that is a good thing: instead, you create an app password, which only sends emails and can be revoked at any time without changing your main password.
Before you start
An app password only exists for accounts with 2-Step Verification turned on. If you haven't turned it on yet, do it first at myaccount.google.com, in the Security section. It is worth it in any case: it protects your account from break-ins.
Creating the app password
- Open myaccount.google.com/apppasswords and sign in to your account, if asked.
- Give it a name that will help you recognize it later, for example "Libtro Kindle".
- Click Create. Google shows a 16-letter password.
- Copy that password and paste it into the App password field in Settings → Kindle in Libtro. The spaces don't matter.
Google shows the password only once. If you lose it, just create another one.
Security
- In Libtro, the app password is stored encrypted and is never shown on the screen again.
- If you want to cut off access, delete the app password on the same Google page. Your main password stays the same.
- Never enter your regular Google account password on any site other than Google's own.
Using another provider?
Outlook, Yahoo and others also offer app passwords or SMTP. In Libtro, open Email server (advanced) in the Kindle settings and enter the server and port given by your provider.