Did you do it like this: I presume you have already set up to use imap. Logon to gmail webmail account and under 'SEttings > Forwarding/ Pop & Imap Select to enabled IMAP and save settings.

Do not use 2 step verification - do not generate any app specific password.

As you haev already attempted to set up via Thunderbird. Please try forcing gmail to unlock Captcha - it will be a link like this:

https://www.google.com/a/YOURDOMAIN/UnlockCaptcha

I think the following is only ordinary gmail account : https://accounts.google.com/DisplayUnlockCaptcha

In Thunderbird check the cookies:

• Menu app icon > Preferences > Privacy & Security

Under 'Web Content'

• Select 'Accept cookies from sites'
• Select: Accept third party cookies'
• Keep until 'Expire'
• Click on 'Exceptions'
• Address of web site - enter: https://accounts.google.com
• Set to 'Allow'
• click on 'Save Changes'

In Thunderbird

• Menu app icon > New > Existing mail account
• Enter name
• Enter full email address
• Enter Password - same password you would normally use to access via gmail webmail - do not use an app specific password because you are trying to use OAuth2.
• Select checkbox to remember password

If the 'Continue' button is not working - not finding settings - try the 'Config manually' option But it might work this time after doing the unlock captcha, so gmail logs your computer.

• Click on 'Configure manually.. ' button

Incoming: Protocol: IMAP Server: imap.gmail.com Port: 993 Connection SEcurity: SSL/TSL Authentication Method: OAuth2 User name: full email address

Outgoing: Server: smtp.gmail.com Port: 465 Connection SEcurity: SSL/TSL Authentication Method: OAuth2 User name: full email address

click on 'Retest' If all ok then click on 'Done'

please check you are not using a VPN - google will not work with a vpn.

Some Anti-Virus products now come with a VPN. I use Norton and after an update discovered it has installed and switched a VPN. I switched it off and all functioned again.