I presume you mean Thunderbird is working and you can see mail accounts, but it cannot get access to the server to get emails. First check that Thunderbird is in 'online' mode. Do you see a 'two blue screen' icon in the bottom Status Bar on far left? If yes, you are in online mode. If no, you see a 'two black screen' icon, then you are in 'offline mode' and therefore cannot connect. Click on that 'two black screen' icon to revert to online mode. If you are in online mode and cannot send nor receive emails in Thunderbird and this occurred after an update, then it is possible that Thunderbird is being blocked by your Firewall. the Firewall may be part of your Anti-Virus package. Close Thunderbird. Access Firewall and make sure Thunderbird is in the list and it is allowed. Once I had to block. ok it and then access again and set to allow.