When you ask a question, it's important to add information to suppliment the question. What OS do you use? Windows , MAC, Linux ? What version of Thunderbird are you using ? Are you talking about a Pop or Imap mail account ? What server settings are you using for incoming and outgoing ? You can upload images that show that data found in Account Settings OR you can also find it in Help > TRoubleshooting Information - scroll down to Mail and News Accounts section - post image or copy and paste the data. What error message do you get when you try to 'Get Messages' or Send email ? We need it word for word verbatim or upload an image showing the error. In the meantime check the following because they could be blocking access: On computer check you have the following: '''Firewall:''' Access Firewall - it might be the default on computer or controlled by an Anti-Virus prgram. Set up the Thunderbird program as 'allowed' so nothing gets blocked. Do not just switch it off because if controlled by an Anti-Virus then the default one on Windows takes over. Confirm Thunderbird is set up as allowed program. '''VPN:''' Check computer for a VPN. Some Anti-Virus products now offer a VPN and I have come across some people who did not realise one had been enabled. Switch off VPN. Many servers do not like VPN as it atempts to hide your IP address, so server decides you might be hacker so it auto blocks access. Confirm VPN is switched off