To diagnose problems with Thunderbird, try one of the following:

• Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.
• Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

Thanks so much GamerFreak for your kind assistance. Unfortunately both the remedies did not yield any success.

I am still not able to download any new email.

This issue specifically cropped up once I updated to v31.3.0 Before the update, everything was working fine. My colleague, who was still on v24.6, reported that his email was working fine. The moment it updated and he restarted Thunderbird, the problem surfaced. This issue repeated on 6 other machines that had updated to v31.3.0, so I wonder what could have changed to cause this.

Certain Thunderbird problems can be solved by performing a Clean reinstall. This means you remove Thunderbird's program files and then reinstall Thunderbird. Please follow these steps:

1. Download the latest version of Thunderbird from http://www.mozilla.org/en-US/thunderbird/ and save the setup file to your computer.
2. After the download is complete, close all Thunderbird windows (Click Exit/Quit from the menu button on the right).
3. Delete the Thunderbird installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Thunderbird\
     • C:\Program Files (x86)\Mozilla Thunderbird\
4. Now, go ahead and reinstall Thunderbird:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to open Thunderbird after clicking the Finish button.

WARNING: Do not run Thunderbird's uninstaller or use a third party remover as part of this process, because that could permanently delete your Thunderbird data, including but not limited to, extensions, emails, personal settings and saved passwords. These cannot be recovered unless they have been backed up to an external device!

Please report back to see if this helped you, but if it didn't I would then suggest to go back to latest version *that worked for you* and wait until the next update. Please tell me what worked for you and please select this as the solution. This will help other users with similar question find the solution more easily.

Thank you for contacting Mozilla Support.

Thanks again for your quick reply. I did as instructed but no luck there. May I know how to download the previous version (v24) ? Appreciate if you could point me to the link. Have been searching but most of the sites (e.g. CNET's, softonic, etc) list only the latest v31 install file.

Well it looks like this website has it. http://ftp://archive.mozilla.org/pub/.../releases/ It's not in the folders, if you look at the bottom it says latest release (24) even though its not, it's still there. This website should help you install it, http://www.ghacks.net/2009/08/01/how-to-download-old-firefox-and-thun... Please let me know if it works and if it does please select this as the solution to help other people because I know this can be a hassle. I hope it all works and again if it doesn't just let me know.

Yes!!!

Reverting to ver 24.6 completely solved the problem! Woohoo!

Hopefully the developers can have a look at what changes were made to ver 31.3.0 that made it unable to work. My mails are hosted on Gmail servers, so I'd reckon many people would face this issue as well.

Well I am glad it worked, like you said hopefully they can figure out what happen, I hope that your experience with Mozilla will be better next time, Have a happy new year.