What leads you to assume this is a Thunderbird bug, and not a network, server, firewall, or email provider issue?

Which provider?

yes its Thunderbird issue because my gmail id is working with same application....

So that tells you that a different client probably using a different protocol and possibly a different server and almost definitely different routeing is working.

Most issues of this type are transient. Try again later.

I use Thunderbird with gmail on Windows 10 and MX Linux. I see no persistent issues with gmail on either of those platforms. I get about as much hassle on my Android tablet. If my Android imap/pop/smtp client struggles with my gmail accounts, then I try the native Android gmail app. If that works better, I am led to think that gmail's pop/imap/smtp server is in trouble, not specifically Thunderbird.

imranahmad said

yes its Thunderbird issue because my gmail id is working with same, its yahoo provider

its yahoo provider i have Allow apps t.hat use less secure sign-in apart of that issue has been occurred.

Yahoo has issues they are working on. https://mobile.twitter.com/YahooCare/status/887473724991053825

has issue resolved or not..?