Globally Registering SOGo as a MailHandler on Windows TerminalServer (automatically fill in the right username)

I would like to automatically register SOGo in Chrome as the mail-handler for mailto links in chrome. so the only thing not working currently is to automatically use the logged in user (the user which is logged in windows OR the user which is loggs in SOGo)

this is the URL I registered: https://mail.mydomain.tld/SOGo/so/%username%@mydomain.tld/Mail/UIxMailPopupView#!/Mail/0/new?%s

this works except for the "%username%@mydomain.tld"-part. what variable can I use so I don't need to do this on a user-basis?