We using exchange 2013 for are long time, but someday I try test my mail server (at https://www.mail-tester.com/) and fond some errors, most of it I fix, but left some. Most what I do not understanding is error - "FORGED_RELAY_MUA_TO_MX" I found some description about, needed to add header "X-Spam-Relays..."
x-spam-relays-trusted: x-spam-relays-untrusted: x-spam-relays-internal: x-spam-relays-external:
First of all, we do not use relay, it is just disabled as default at our server So that's why I can't understand what I must use here. Added header is not are problem, but what I must wrote at it...
Is there a problem with your normal email sending and receiving? According to my research on the information you provided, I did not find any introduction to these properties in Exchange. If your Exchange currently does not have any functional problems, I think it is not a good choice to add it at will. Please make sure that the SPF, DKIM and DMARC in your DNS records are set correctly. This will reduce the reception of spam in your mailbox server and reduce the possibility of rejection of your email. Please refer to: Understanding SPF, DKIM and DMARC