Recieving an error message on an email client like Outlook, Mac Mail etc, even though password is correct?
Gmail recently enforced a higher security sign in procedure no longer using OAuth as the default access method. While developers have received warning from Google, not all email clients and apps have been updated to use the new protocol.
To allow your email client apps to continue to sign in to Gmail the old way, you need to turn on access for these “Less secure Apps” in your Gmail security settings.
Help article: Allowing less secure apps to access your account