It would be helpful to know what the 'blah blah' actually said. There are some anti -virus products like AVG or Avast that use the words "concurrent connection limit" , but it is possible to mean you have exceeded the number of concurrent connections to the server. In thunderbird you can reduce the number of connections. * Right click on the account name folder in Folder Pane and select 'Settings' * Select 'Server Settings' * Click on 'Advanced...' button * For 'Maximum number of server connections to cache' reduce the number to 3 (you may need to reduce to 1) * click on OK. * Under 'Server Settings' suggest you increase the number of minutes for checking for new mail - not less than 10. * click on OK Connections need to close and sometimes the server is not exactly as quick to recognise connection has been dropped. Note: if you have a phone that you use to connect to mail account, it may also have opened connections. The server will only allow x number of connections and that means Thunderbird and phone are included in total. Apple phones are well known for not disconnecting. If you have another computer also connecting then you need to do the same. Please switch off phone to force connections to disconnect. Exit Thunderbird on all computers that connect to the server and wait a while (whilst you have a cup of coffee) to ensure connections have been dropped by the server. Then restart Thunderbird.