In the documentation (Bounce handling - Configuration) for v6 you find:
Try to unlock your GMail account, sometimes GMail blocks the application: http://www.google.com/accounts/DisplayUnlockCaptcha
If you are already using 2-Step Verification, Google will show you the following link https://support.google.com/accounts/answer/185833?hl=en&ref_topic=7189145
Here you can generate a password for your IMAP (others). Note that you can use the same for SMTP and Joomla SMTP.
There isn't any need to switch off your 2-step verification and use "Authorize less secured applications"
/Robert
