rer :The server responded: Try again later, closing connection.. That is a specific message from the server not Thunderbird. It sounds like the server is having a problem. Maybe the server is undergoing maintenance or suffering from high traffic. But as you have not provided any information about your set up nor what server you are trying to access. You could check to see if the server is down right now or see if the website of company that provides server has any info on known issues. In the meantime I suggest you check the following on your computer: '''Firewall:''' The Firewall may be controlled by the default one that came with the OS or it might be controlled by an Anti-Virus you installed. Access the Firewall and set up the Thunderbird program as 'allowed'. It's important to have Thunderbird set up as an allowed program to ensure nothing ever gets blocked. Confirm: Thunderbird is set up as allowed program in Firewall. '''VPN''' Please check your computer for any VPN. Some OS now include a VPN and many Anti-Virus products now offer a VPN. I have come across people who discovered they had a VPN that was enabled which they did not realise. So please double check computer - if you have a VPN enabled then switch it off because srevers do not like VPN as it hides your IP address so they think a hacker is trying to to access your account and so they block access. If you insist on using a VPN then you must set up a split tunneling and set up Thunderbird to use it.