<Domain_URL> #5.7.1 smtp;554 5.7.1
<clientemailaddress>: Relay access denied
When an Office 365 user tries to send an email message, the Office 365 user may receive an NDR that resembles the following:
<Domain_URL> #<<Domain_URL>#5.4.6 smtp;554 5.4.6 Hop count exceeded -
possible mail loop> #SMTP#