Thanks Prathapml In the registry, I've seen that "ReinstallCommand"="\"C:\\Program Files\\Mozilla Thunderbird\\thunderbird.exe\" -silent -nosplash -setDefaultMail" I try to launch this command. It works well, but a very little window (we can just see the title bar) of thunderbird stays open. After that, thunderbird is the default mail client and the shortcut in the start menu is ok. I haven't find an help about the parameters for thunderbird.exe. -h or --help doesn't works