Slightly OT: Postfix smtpd restrictions

Drew Marshall drew.marshall at
Fri Jun 25 09:01:47 IST 2010

On 24 Jun 2010, at 12:57, Jason Ede wrote:

> This is purely MTA based, but since a lot of users here run postfix...
> How have others found reject_unknown_reverse_client_hostname and the  
> more harsh reject_unknown_client_hostname  in postfix? I’m debating  
> implementing them here and wonder if others have found them  
> problematic or useful? I thinking they should be good for weeding  
> out spam emails and I can’t see that they should catch legitimate  
> senders, but want to be sure

I have to be honest, I ran this for a short while in warn mode and  
found that the number of people with mis-configured PTR records is  
huge (In the UK). For example, BT won't let anyone change their PTR,  
so EHLO/ HELO is always going to be a mismatch for these. Most people  
running Exchange 'naked' to the Internet end up having a EHLO as  
<name>.local or some such other non existent TLD so that ends up not  
matching either and so it goes on.

As ever YMMV but for me, I found other ways to combat spam coming from  
these sorts of connections such as RBLs etc.


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