a customer is trying to send me a email but gives in my postfix log:
NOQUEUE: reject: EHLO from mail.domain.pt[xxx.xxx.xxx.xxx]: 450 4.7.1 <otherdomain.pt>: Helo command rejected: Host not found; proto=SMTP helo=<otherdomain.pt>
Jul 21 22:19:50 myserver postfix/smtpd[7978]: disconnect from mail.domain.pt[xxx.xxx.xxx.xxx]
The customer insists that the problem is in my postfix, not on their side but from my understanding, it is a domain configuration problem from their side. This is part of main.cf:
smtpd_recipient_restrictions =
permit_sasl_authenticated,
permit_mynetworks,
check_client_access hash:/etc/postfix/rbl_override,
check_sender_access hash:/etc/postfix/sender_access,
reject_unauth_destination,
reject_invalid_hostname,
reject_non_fqdn_sender,
reject_non_fqdn_recipient,
reject_unknown_sender_domain,
reject_unauth_pipelining,
permit
# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.
smtpd_helo_restrictions =
permit_mynetworks,
reject_invalid_hostname,
reject_unknown_hostname,
reject_non_fqdn_hostname
How can i prove that it is a problem on their side? How can i make tests? Usually, when i get this error in the postfix log, is a spam or a fake email. Thank you for your help.