Hello there detaill. We have read your message. We try to help you. How long is the few years ago? Did you changed somewhere from pc or ssd or hd in the beginning or recent? Thunderbird stores your maps on the harddrive of your computer machine. Maybe you had a usb with backups or copies of them? All the passwords and logins are oke? Your emails are a part of the profile maps in the Mbox files or map that belongs on your ssd that’s where Thunderbird ''stores'' your mails. You can find them in the same place around the profile maps. Yes in Windows systems are hidden files or maps as a option possible. My Computer>'''X drive'''>Tools menu>Folder Options>Viewn tab, tick "Show all hidden files and folders”. Sometimes there can be a huge storage under a simple file character. But also on your harddrive. If you had changed your harddrive in the past then there will be no email for you anymore. The Thunderbird server holds your mails on the server it is called imap storage. In settings you can choose if the message stays on the server or just being deleted after startup from Thunderbird to read the new inbox mail. The mails stays in or on the server for various times. Pop3 is also storage in a map for mail but this process belongs on your pc. Most of the people uses imap in 2021. For server settings go to account settings>server settings there are more options there to configurate this. If you deleted your pop 3 account before beginning the imap account and accidently delete all of the pop 3 account to start with the new account , all your message s will be gone. https://support.mozilla.org/en-US/questions/1216773 Greetings Firefox volunteer.