|I guess you can't, except, you have configured the desktop for e.g. Remote Desktop Connection.|
Is so, hopefully the desktop is behind a firewall router.
In that case, you have hopefully configured the router, to forward the port for Remote Desktop Connection to the Desktop PC.
I guess it's not configured, so there is no chance to do that.
So you need someone, how can e-mail the addresses to a mail address, accessable from the internet, e.g. gmail, gmx, hotmail a.s.o.
Then you can login to the internet mail provider, look into the received mails and get your addresses.