Send Message Fails

Question

When I try to send a message, a dialog appears that says "Status: Assembling message . . .", then after a few seconds, a Send Message Error dialog appears that says "Sending of message failed. Please verify that your Mail & Newsgroups account settings are correct and try again."
1. The "Status: Assembling message..." dialog never used to appear and the emails went out fine.
2. I have checked the account server settings and they ARE correct. I tested them and the server likes them. Error message fails to specify exact cause of failure, so it is of no help.
3. I removed my user account and recreated it. Same problem, except now my archives and inbox are empty. (Fortunately, I copied my Profile files to a backup location, so I suspect I may not have lost everything if I can figure out how to restore the data files and get TB to recognize the restored files.)
4. I uninstalled the program and reinstalled it. Same problem, didn't fix it.
5. I created a new account on a different server. Access codes test out properly. Same problem, doesn't send. My hairstyle looks terrible now after my pulling numerous patches of it out.
I have done everything except give up and go to another email program and try to import my data or just start over. Solution is probably simple, but so deep in the hidden guts of the program that I can't find it.
Where's the problem, and how do I correct it??

Answer 1

To diagnose your problems with Thunderbird, try he following:
*Restart the operating system in '''[http://en.wikipedia.org/wiki/Safe_mode 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: [http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-including-safe-mode Windows 8], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-7 Windows 7], [http://windows.microsoft.com/en-us/windows/start-computer-safe-mode#start-computer-safe-mode=windows-vista Windows Vista], [http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/boot_failsafe.mspx?mfr=true" Windows XP], [http://support.apple.com/kb/ht1564 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.
In this case I would put money on it being the anti virus. The most troublesome at the moment is Avast, but they all block outgoing connections from Thunderbird at different times and disabling email scanning, or SPAM filters, or enabling access in the firewall component or a combination of all of the above can be required.
Safe mode identifies the probable source if things would as they should. It may also only be the account setup process the A/V messes up as well. Thunderbird makes many connection attempts when scanning for settings when they are not in the database (Or connection to the database is blocked by the Anti virus program) and the anti virus just does not faithfully report the results so you get silly error messages.