Overview

Mail source headers are providing extended information about the Kerio Connect mail server. If the SMTP server option called Hide local IP in Received headers is checked, the Kerio Connect can replace the internal IP address.

Diagnosis

When the 'Hide local IP in Received headers' option is enabled, the Kerio Connect server hides the IP address of the sender and replaces it with 'localhost ([127.0.0.1])'.

Example of a message without Hide local IP enabled:

Received: from [192.168.1.35] ([192.168.1.35])
 (authenticated user user13@kerio_domain.com)
 by mail.kerio_domain.com (Kerio Connect 9.2.12 patch 1) with ESMTPSA
 for user12@kerio_domain.com;

Example of a message with Hide local IP enabled:

Received: from localhost ([127.0.0.1])
 by mail.kerio_domain.com (Kerio Connect 9.2.12 patch 1) with ESMTPSA
 for user12@kerio_domain.com;

For the extended output between 2 mail servers, it's advisable to enable 'SMTP client' and 'SMTP server' options in Debug logs. For more information, please refer to Selecting Debug Log Messages to Display.

Debug logs can show the detailed intercommunication between two STMP servers. It might be the scenario when the second server (remote part) does NOT have a similar Hide local IP option enabled. If that is the case, the local internal IP address of the remote host will be shown in the SMPT client output.

{smtpc} Connecting to server 192.168.20.1 (192.168.20.1:25) using local interface 0.0.0.0 ...
{smtpc} Connected to SMTP server 192.168.20.1
{smtpc} Received greeting: 220 mail1.remote_server.com ESMTP ready

Solution

As the best-practice, we recommend enabling Hide local IP in Received headers option as it protects your Kerio Connect installation from spammers.