Test Email filter error

I think that since I updated in 66 version I can't test any email filter from cPanel. I get an error like this

Code:

Error: The “/usr/sbin/sendmail” command (process 20084) reported error number 1 when it ended.

What is the correct way to debug this, where should I start searching? Google wasn't impressed with my queries..

 

Thank you Michael for your reply I would prefer to try first and debug this before opening a ticket. Opening the

Code:

/usr/local/cpanel/logs/error_log

I noticed at the same time of the error this:

Code:

failed to expand "${lookup{$interface_address}lsearch{/etc/mail_reverse_dns}{$value}{$primary_hostname}}" (smtp_active_hostname): failed to open /etc/mail_reverse_dns for linear search: Permission denied

The permissions of /etc/mail_reverse_dns are set to 640 (root/mail == user/group)

Does it seem like a system permissions issue?

 

Changing only the permissions to 0644 resolved this issue. I've left the user group as it is (Should I change it?) I'm wondering what caused this in the first place and set it to 0640. I'm on CENTOS 6.9 kvm, WHM v66.0.19

 

The only instance of this is at smtp_active_hostname which is set to

Code:

${lookup{$interface_address}lsearch{/etc/mail_reverse_dns}{$value}{$primary_hostname}}

How should this line be?