I need to ask a few questions to understand the current situation. re : lost my app for Mozilla thunderbird What OS are you using? Did you need to reinstall the OS? Did you need to reinstall the Thunderbird program ? Where did you get the download for the Thunderbird program eg: from official webpage here: https://www.thunderbird.net/en-US/thunderbird/all/ or via the Windows app ? Check Firewall: Exit Thunderbird if running Access Firewall - it might be the default that comes with computer or it might be controlled by an Anti-Virus product you installed. Thunderbird must be set up as an allowed program otherwise it might get blocked by Firewall. We need to rule out this as the issue. So, please confirm - Thunderbird has been set up as an allowed program. If yes, you needed to reinstall the OS Did Windows OS create a folder called 'windows.old' on the C: drive ? If yes: Select that 'windows.old' folder to see contents. Does that 'windows.old' folder contain something in this location: C://Users/Username/Appdata/Roaming/Thunderbird/..... OR if you installed program using Windows app store: The Microsoft Store version is located in a different place. C://Users/UsernameAppData\Local\Packages\MozillaThunderbird.MZLA_h5892qc0xkpca\LocalCache\Roaming This will tell if all your profile etc has been saved and can be recovered. When you run Thunderbird, does it locate your old profile and emails etc, but then fails to connect to server? If yes: What have you got in this location: In Thunderbird Help > Troubleshooting Information Scroll down to 'Mail and News Accounts' Copy all data and paste into this question. If you reinstalled Thunderbird and now you are asked to create a new mail account in a new profile but having a problem.... Please post an image showing what it shows when you are trying to create the account. Tell me what server you ar trying to connect to...eg: Comcast, BT, yahoo, gmail etc Please check current password: Please attempt to logon to your webmail account via a browser using the password you believe to be correct. If you get access, then you know your password is accurate. Do you get access to your webmail account?