There is a tutorial here but it didn't work for me.
I mean I cannot add a Mail shortcut to my StartUp folder by dragging and dropping. Is there any other way?
you cannot drag the mail shortcut from the startmenu. Instead you need to create a desktop shortcut. You can do this by doing
Windows + R to open the RUN menu and then typing
shell:AppsFolder to open the apps folder. From there you can search the apps folder for the mail application. Right click on the application and click create shortcut, this will prompt you to create a shortcut on the desktop, click yes. Now there should be a shortcut for the mail app on your desktop that you can drag into the startup folder.