As you did not bother to respond in your[https://support.mozilla.org/en-US/questions/1427743 previous topic] on this issue I wonder why you are raising it again. There are a myriad of things that can cause an inability to write to the mailbox, which is a file on your computer. The most common is you antivirus program locking the file while is scans it. But there are plenty of other caused of file contention as a google search would show. So when will someone fix it for you? Never as you are the only one who has access you your device and your software. I would suggest you start by trying the following fairly standard diagnostic steps to try an isolate the cause. #* Does Thunderbird work as expected in [[Troubleshoot Mode Thunderbird|Thunderbird troubleshooting mode]]? #* Does Thunderbird work as expected with your OS started in '''[http://en.wikipedia.org/wiki/Safe_mode safe mode with Networking]'''. Instructions for each operating system: [https://support.microsoft.com/en-us/windows/start-your-pc-in-safe-mode-in-windows-92c27cff-db89-8644-1ce4-b3e5e56fe234 Windows 10/11], [https://support.microsoft.com/en-us/windows/windows-startup-settings-including-safe-mode-7f31dcea-6427-0ba0-ec1b-729a56321cd3 Windows 8], [https://support.microsoft.com/en-us/windows/advanced-startup-options-including-safe-mode-b90e7808-80b5-a291-d4b8-1a1af602b617#start-computer-safe-mode=windows-7 Windows 7], [http://support.apple.com/kb/ht1564 OSX]