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Odd problem with Postfix and reject_unknown_client option

I have a strange problem with Ubunto 8.10 (Intrepid Ibex) and Postfix. In the interest of cutting down spam, I've been using the reject_unknown_client configuration setting. According to the docs, this will reject mail from servers with no PTR (e.g. reject virtually all dynamic-server stuff).

I'm getting a few issues. For example, in my log today:

Quote:

Nov 13 08:34:22 osprey postfix/smtpd[23740]: NOQUEUE: reject: RCPT from unknown[195.74.102.190]: 450 4.7.1 Client host rejected: cannot find your hostname, [195.74.102.190]; from=<bounce@senderdomain.net> to=<myemail@mydomain.co.uk> proto=ESMTP helo=<partners.enta.net>

Quote:

Nov 13 08:34:23 osprey postfix/smtpd[23749]: NOQUEUE: reject: RCPT from unknown[84.234.16.230]: 450 4.7.1 Client host rejected: cannot find your hostname, [84.234.16.230]; from=<adsl24@adsl24.co.uk> to=<myemail@mydomain.co.uk> proto=ESMTP helo=<server.adsl24.co.uk>

Yet the host command gives these responses:

Code:

root@osprey:~# host 195.74.102.190

190.102.74.195.in-addr.arpa domain name pointer partners.enta.net.

root@osprey:~# host partners.enta.net

partners.enta.net has address 195.74.102.190

Code:

root@osprey:~# host 84.234.16.230

230.16.234.84.in-addr.arpa domain name pointer server.adsl24.co.uk.

root@osprey:~# host server.adsl24.co.uk

server.adsl24.co.uk has address 84.234.16.230

So, as far as I can tell, Postfix shouldn't have had any issues.

Am I missing something?

Many thanks,

Jim

Assuming you are using >=2.3, try using reject_unknown_reverse_client_hostname instead and see what happens.

Many thanks for the quick reply, I appreciate you taking the time.

I'm using 2.5.5, so I've changed my entry to:

Quote:

smtpd_client_restrictions = hash:/etc/postfix/client_restrictions,reject_unknown_helo_hostname,reject_unknown_reverse_client_hostname

Does this look to be safer?

Jim

My suggestion was more that the change I suggested limits the rejections - you can narrow down the cause this way.

Try sending an email from one of those senders that failed before and see what happens.

Many thanks.

I'm have to wait for one of the "problematic" senders to send me an email, as I'll want it to be a realistic test.

Thanks again for your help.

Jim

That's OK. In the meantime, read up of the differences between reject_unknown_client_hostname and reject_unknown_reverse_client_hostname at http://www.postfix.org/postconf.5.ht...lient_hostname