Can't send mail. Error message states mail server sent an incorrect greeting

I do not have the Secure VPN application.  I have disabled it in the try as per the article and that did not correct the issue.  Is there an easy way to uninstall and re-install?

Thank you Dinesh.  After a week of tracking this, it appears to always be available after 4pm my time.  3:57pm and I get the message.  Can't believe that it has anything to do with Thunderbird either.  I am pursuing this with Comcast.

Hello Barry,

We should check whether AVG program is the reason behind this.
Please disable AVG Internet Security temporarily as mentioned in this article and check the status.
You can also turn off AVG Secure VPN and check the status with the email.
Keep us informed about the status.

You can try reinstalling AVG at your convenient time, Barry. However, this issue seems to be dealt with your service provider or Thunderbird. 
Thank you for your understanding in advance!

Thank you for trying, Barry.

It seems that it is not caused by AVG as you've disabled AVG and the issue persists.

However, I suggest you to uninstall AVG Internet Security from control panel and check if you're able to send emails.

Refer the article for https://support.avg.com/SupportArticleView?urlname=Uninstall-AVG-Internet-Security

This started soon after I had started my subscription to Ultimate Security.  Using Thunderbird, and the last part of the error message has "Excessive failed authentication.  ESMTP server temporarily not available".  I have not had any changes other than this in a long time.  Thanks for any help you can provide.

I do not have the Secure VPN application.  I have disabled it in the try as per the article and that did not correct the issue.  Is there an easy way to uninstall and re-install?  

You are most welcome, Barry.
If you are using AVG Secure VPN, turn it off and check the status with the email.
If the error doesn't appear, then change the location in AVG Secure VPN and see for which location the issue gets resolved.

Thank you Dinesh.  After a week of tracking this, it appears to always be available after 4pm my time.  3:57pm and I get the message.  Can't believe that it has anything to do with Thunderbird either.  I am pursuing this with Comcast.