We just had a customer complaining about his thunderbird application not being able to connect to his gmail account that he had for ages without any issue!
Upon investigation we found that he had his new Android tablet set up with the same gmail account recently. Google always looks out for any hacking activity so if there are multiple clients (thunderbird and Android’s email) trying to access the same Google account it is quite possible that Google decides to block one/some of them or all.
This is how you enable the account again in the client (thunderbird in this case).
Step 1. Switch off Thunderbird in your PC/laptop if it’s still running.
Step 2. Now open your GMAIL through browser by visting www.gmail.com
Step 3. On top right you will see the Settings icon (looks like a gearbox in the new Google set-up) – click on Settings from drop down.
Step 4. Click on the tab Forwarding and POP/IMAP.
Step 5. Disable POP or IMAP whichever is giving you the hassle.
Step 6. Now visit this link from Google and follow through the instructions.
Step 7. Enable POP/IMAP again (same as Steps 3, 4 above) from GMAIL interface.
Step 8. Restart thunderbird. It should work now.
Hope this helps everyone who faces similar problem in future!