It may be a temporary error that will resolve itself tomorrow.

Some steps you can try. Between each step, see if Thunderbird works any better.

1. Reboot the computer. Never underestimate the problems that can be solved by simply rebooting a computer, especially if that computer has Windows.

2. 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.

3. Restart Windows 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 10, Windows 8, Windows 7, Windows Vista, Windows XP

If Thunderbird works OK when Windows is running in Safe Mode with Networking, but doesn't when Windows is running normally, then another process/program is interfering. The first thing to look at in this case is the security software on the computer. That means the Firewall and Antivirus programs. Open them up, tell them to update themselves, both the program and their antivirus definitions.

Thank you Johnson for sharing your thoughts....

I tried your suggestions.. But the problem still continues..

As you have mentioned, hope this is a temporary problem and will get resolved by itself shortly ...

It has been a couple of days. I am curious if your problem is resolved.

Hi Bruce,

"Technically" the problem didn't solve ....

After my previous post, I waited for 2 days, but the problem was not resolved.. Then I tried to run the previous versions of Thunderbird after installing the running version of 45.6.0 along with Profile folder... The latest version 45.6.0 and 45.5.1 showed same problem...

Finally, I tried my luck with Version 50.0 and, to my surprise, this is working fine for the last 3 days without any problems... :))))

I'm glad the beta version is working for you. In general I do not recommend beta versions of programs to regular users, only to expert computer users who want to help report problems with the beta versions.

This 50.0 beta version is working fine for now...

I hope the real problem with 45.6.0 version will be resolved and I can start using the latest and upgraded version.

I hope the real problem with 45.6.0 version will be resolved

Are you kidding? Do you seriously think there is a general problem in Thunderbird 45.6.0 preventing it from sending messages via Gmail, and you're the only one complaining about it? All hell would brake loose then.

It is much more likely the problem is in your environment. What is your anti-virus software?

I am not blaming 45.6.0 version for flaws.... I still believe that there is some problem with my settings itself... I just hope that some one with same problem comes up with a working solution....

Further, I am not using any Anti Virus software... I was initially using Malwarebytes... But when this problem stepped in, i removed the anti-virus, but no solution was found... I even tried on other PC with no anti-virus also...

vnprabhu said

Hi, I am using thunderbird 45.6.0 version. But today it suddenly failing to receive or send mails... No mails are received even after continuous "refresh" attempts, with no error message surprisingly... While sending getting this error message "The message could not be sent using SMTP server smtp.gmail.com for an unknown reason. Please verify that your SMTP server settings are correct and try again"... I checked for errors in SMTP server, firewall protection etc... All are fine ... Not understanding how this is failure has occurred all of a sudden when every thing was just right till last night???

I am getting this everytime I try sending email.

"Sending of the message failed. The message could not be sent using Outgoing server (SMTP) smtp.xxxxx.com for an unknown reason. Please verify that your Outgoing server (SMTP) settings are correct and try again."

Having the same problem with other domain servers too. Also incoming emails are not getting delivered to my inbox. Till yesterday it was all fine.

@simpleyblack This is a support forum. Thus please start your own thread by asking a new question. Your situation is 99.99% likely to be different than the original poster in this thread.