I replied, hoping that this is ok.
I modified the file "master.cf"as follows:
smtpd_helo_restrictions= permit_mynetworks, warn_if_reject reject_non_fqdn_hostname, reject_invalid_hostname, reject
and I add the proxy server name MX section "network" in the file "main.cf" as follows:
mynetworks = 127.0.0.0/8 [::1]/128, my_serverproxymx
thank you let me know if this is correct.