Multiple computers

I have two computers in my household. One for myself and one for my wife. Have been using Thunderbird email on my computer for a few years with no issue. My wife uses a different email. We both get email from the same server using the same email address. I recently set up a new computer and had to download Thunderbird and synced all my bookmarks from the old. Before this anything each of us did was separate from each other. Now if either of us read or delete an email, it is deleted from the other computer. Once an email is downloaded I need any actions done to that email to be separate from the other computer as it has always been. The version of Thunderbird I downloaded is the same version I had before except it is 64bit rather than 32bit. I have tried all settings but nothing changes this. Any help appreciated.