Google alerts that someone had tried to access my account prompted me to finally change my Google password. I have now verified my settings but still cannot sign into Thunderbird. These are the messages I receive: Enter your password for [email protected] on smtp.gmail.com: Sending of the message failed. An error occurred while sending mail: Could not get password for smtp.gmail.com. The message was not sent. Sending of the message failed. The message could not be sent using Outgoing server (SMTP) smtp.gmail.com for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again. Step 2: Try these troubleshooting steps [I HAVE NO OTHER DEVICES.] Update your email client to the latest version. Use an App Password: If you use 2-Step Verification, try signing in with an App Password. Allow less secure apps: If you don't use 2-Step Verification, you might need to allow less secure apps to access your account. If you recently changed your Gmail password, you might need to re-enter your Gmail account information or completely repeat your Gmail account setup on your other email client. If the tips above didn't help, visit https://www.google.com/accounts/DisplayUnlockCaptcha and follow the steps on the page. The email client's sign-in method might be insecure. Try signing in directly on the Gmail app. Then it says: Account access enabled [this via the DisplayUnlockCaptcha site], but still cannot get in. Please try signing in to your Google account again from your new device or application.