SMTS-500 — Trivial configuration loop danger
Proxy has connected to a forwarder that has introduced itself by hostname and greeting printed in this message. However, the same hostname and greeting uses smtp-proxy when introducing to clients arriving according to session-acl printed.
It is probably a misconfiguration, setting smtp-proxy itself as one of forwarders.
If it is not a loop and all settings are correct, please, use HOSTNAME or SESSION-ACL.WELCOME-MSG configuration directives to change the greeting and break the loop check.