It's obvious you want a fix, but you have to assume no one is sitting beside you and they know nothing about what you can see etc. Please supply information to support the question.

What OS do you use? What version of Thunderbird do you use?

Do you get an error message? If yes then upload an image of the error message OR type the words verbatim.

What server are you talking about? Post the following information In Thunderbird

• Help > Troubleshooting Information
• Scroll down to 'Mail and News Accounts' section
• Copy all the data in that section and paste it into this question in forum OR upload an image file that shows all that section.

If you have solved this issue then please state how you solved or if you still have an issue please respond by providing information and post it into this forum question.

I got in touch with the postmaster at bigpond and was told to turn off VPN and the problem has gone away.