Relay connector for external mail failing

I created a receive connector to relay for external mail.  I set it for anonymous users only and ran the command: Get-ReceiveConnector "Anonymous Relay" | Add-ADPermission -User "NT AUTHORITY\ANONYMOUS LOGON" -ExtendedRights"Ms-Exch-SMTP-Accept-Any-Recipient"

I added my workstation IP address in the allow list to relay email.  However, when I telnet and enter the field for "rcpt to" as xyz@yahoo.com, telnet will error and say "500 5.7.1 Unable to Relay".  It works when use any internal domain recipient.  

Any idea what I'm doing wrong with configuration of the connector?

ms