Hello, I'm sorry to hear that you're experiencing trouble opening attachments from one mailbox in Thunderbird. To troubleshoot this issue, you can try the following steps: Update Thunderbird: Ensure that you have the latest version of Thunderbird installed on your PC. You can check for updates by going to the "Help" menu and selecting "About Thunderbird." Clear cache and cookies: Clearing the cache and cookies of your Thunderbird application may help resolve any temporary issues. You can do this by going to the "Options" or "Preferences" menu, selecting "Privacy & Security," and then finding the options to clear cache and cookies. Disable add-ons: Sometimes, add-ons or extensions in Thunderbird can cause conflicts or issues. Try disabling any add-ons you have installed and see if the problem persists. Disable antivirus or firewall: Temporarily disable your antivirus or firewall software to check if they are interfering with the attachment opening process. If the issue resolves after disabling them, you may need to adjust the settings or exceptions in your security software. Create a new profile: If the problem persists, you can try creating a new Thunderbird profile. This will start Thunderbird with a fresh profile, and you can add your email account again to see if the issue is resolved. Instructions for creating a new profile can be found on the Thunderbird support website. If none of these steps resolve the issue, it might be helpful to provide more details such as the version of Thunderbird you are using, the type of email account, and any error messages you are receiving. This will help the Thunderbird support community provide more targeted assistance.