Mail rejected: Client host rejected: cannot find your hostname

[Benoît Dubé]

Hi,

I'm using zimbra with Postfix as MTA.

I got the following error message which indicate mail rejection based on
hostname not find.

Aug 26 04:05:49 courriel postfix/smtpd[17755]: NOQUEUE: reject: RCPT
from unknown[67.210.171.12]: 450 4.7.1 Client host rejected: cannot find
your hostname, [67.210.171.12]; from=<commu...@fcm.ca>
to=<x...@domain.name.tld> proto=ESMTP helo=<smtp.fcm.ca>

However, the DNS config of the sender's mta looks good. Here are the
reverse resolution and the forward resolution:

bdube@bdube-laptop:~$ host 67.210.171.12
12.171.210.67.in-addr.arpa domain name pointer smtp.fcm.ca.

bdube@bdube-laptop:~$ host smtp.fcm.ca
smtp.fcm.ca has address 67.210.171.12

And for the MX field for this domain, I got:

bdube@bdube-laptop:~$ dig fcm.ca MX

; <<>> DiG 9.7.0-P1 <<>> fcm.ca MX
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 21616
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;fcm.ca. IN MX

;; ANSWER SECTION:
fcm.ca. 900 IN MX 10 smtp.fcm.ca.
fcm.ca. 900 IN MX 40 globalb.mxsave.com.
fcm.ca. 900 IN MX 30 globala.mxsave.com.

;; Query time: 169 msec
;; SERVER: 24.200.241.37#53(24.200.241.37)
;; WHEN: Fri Aug 27 00:12:52 2010
;; MSG SIZE rcvd: 103

Then, what are the other possible causes to have this mail rejected
which are not tested by the commands I have done.

Thanks for your help.

Benoît

[Charles Marcus]

On 2010-08-27 12:15 AM, Benoît Dubé <benoi...@videotron.ca> wrote:
> Aug 26 04:05:49 courriel postfix/smtpd[17755]: NOQUEUE: reject: RCPT
> from unknown[67.210.171.12]: 450 4.7.1 Client host rejected: cannot
> find your hostname, [67.210.171.12]; from=<commu...@fcm.ca>
> to=<x...@domain.name.tld> proto=ESMTP helo=<smtp.fcm.ca>

reject_unknown_client is known to reject legitimate mail, so you should
not use it globally/indiscriminately unless you're ok with that.

--

Best regards,

Charles

[Noel Jones]

On 8/26/2010 11:15 PM, Benoît Dubé wrote:
> Hi,
>
> I'm using zimbra with Postfix as MTA.
>
> I got the following error message which indicate mail rejection based on
> hostname not find.
>

> Aug 26 04:05:49 courriel postfix/smtpd[17755]: NOQUEUE: reject: RCPT
> from unknown[67.210.171.12]: 450 4.7.1 Client host rejected: cannot find
> your hostname, [67.210.171.12]; from=<commu...@fcm.ca>
> to=<x...@domain.name.tld> proto=ESMTP helo=<smtp.fcm.ca>
>

Yes, this was rejected by reject_unknown_client_hostname.

Yes, it appears the client's DNS is working correctly /now/.

The mail was deferred with a 450 code. This implies that
there was a temporary DNS error of some type. Just because
dig works now doesn't guarantee that it worked when postfix
asked earlier.

You can look in the log for warning: messages from the
postfix/smtpd[17755] process that proceed the reject message.

-- Noel Jones

[Stan Hoeppner]

Noel Jones put forth on 8/27/2010 8:58 AM:

> Yes, this was rejected by reject_unknown_client_hostname.
>
> Yes, it appears the client's DNS is working correctly /now/.
>
> The mail was deferred with a 450 code. This implies that there was a
> temporary DNS error of some type. Just because dig works now doesn't
> guarantee that it worked when postfix asked earlier.

If the OP isn't currently running a caching DNS resolver on his MX, I'd
suggest he do so. It helps curb many of these transient DNS lookup
failures. I installed pdns_recursor on my MX a while back and it has
helped quite a bit with issues similar to this one. Doing so also
decreases lookup latency which can increase performance a bit.

--
Stan