efa-project.org

Usually header of received messages contains reverse resolution of sender mailserver as in this example :

Received: from posta.gemmo.com (posta.gemmo.com [85.18.107.12])
by EFA.gruppocomet.it (Postfix) with ESMTP id 90D13A0680

ping -a 85.18.107.12
posta.gemmo.com [85.18.107.12] con 32 byte di dati:

But in this case there is not resolution, it tell me unknown, but ping -a give me correct resolution so reverse ptr is set but efa was unable to resolve :

Received: from mail.e-integrationservice.net (unknown [83.221.116.117])
by EFA.gruppocomet.it (Postfix) with ESMTP id 58374A006D

ping -a 83.221.116.117
host117-116.static83.221.interbusiness.it [83.221.116.117]

SOLVED

THis is maillog :
EFA postfix/smtpd[27776]: warning: 83.221.116.117: hostname host117-116.static83.221.interbusiness.it verification failed: Name or service not known
Dec 13 06:04:47 EFA postfix/smtpd[27776]: connect from unknown[83.221.116.117]

This occurs when the sender ip doesnt have an A record that match ptr record :
83.221.116.117 resolves to hostname host117-116.static83.221.interbusiness.it
But hostname host117-116.static83.221.interbusiness.it doesnt solve to anything