Usually you will need to enter https://domain.com/RDWeb/Feed/Webfeed.aspx but you could also use email addresses instead of this not too easy to remember URL. For this to work, you don’t need to do anything on your RDS Server but on your DNS.

Add the following Text record to your DNS:

Record:   _msradc
Text:   https://host.domain.com/rdweb/feed

When configuring a new RemoteApp and Desktop connection using email addresses, the tool will contact your DNS which will return the correct value for the configuration.