Local servers will look for remote servers using a DNS lookup on the remote domain's SRV record. In the following example, the record tells Sylow servers to send all requests for this domain to sylowsrv.example.com:8080:
_sylow._tcp.example.com. 86400 IN SRV 10 100 8080 sylowsrv.example.com.
In this way, someone can host their Sylow server on a separate subdomain and/or port from the rest of their site, but still have simple entity names like jake@example.com.
If the remote domain in question does not have a Sylow SRV record, the local server assumes it is at the root at port 80, i.e. example.com:80.
From @peakwinter on June 6, 2017 16:36
sylowsrv.example.com:8080:_sylow._tcp.example.com. 86400 IN SRV 10 100 8080 sylowsrv.example.com.jake@example.com.example.com:80.Copied from original issue: SylowTech/sylow#34