Message Bounced for Domain with no A record

James Day

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Jan 16, 2014, 6:52:17 AM1/16/14

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Hello Postfix User List,

I have a mail server that I use to provide a smart host service for my customers. I have a problem sending a message onto a recipient in the domain cbhc.uk.com. The failure message is below.

I'm struggling to work out why postfix is unable to forward this message when there is a valid MX record.

The error states that there is no A record for the domain name (which is correct) but I would have thought Postfix should be looking for an MX record as well.

I have checked /var/spool/postfix/etc/resolv.conf and confirmed that this contains valid DNS servers (8.8.8.8 and 8.8.4.4) and have confirmed that I am able to query for MX records (using dig) and I get correct results - I have also tested telnet on port 25 to each MX and confirmed I can connect.

I have replaced any potentially sensitive data in the mail log entry whit HIDDEN - I hope this doesn't hamper any efforts to help.

Any help would be greatly appreciated.

Mail log entry:

Jan 16 10:59:52 smtp postfix/smtpd[21012]: B905D39A041E: client=HIDDEN, sasl_method=LOGIN, sasl_username=HIDDEN

Jan 16 10:59:52 smtp postfix/cleanup[21008]: B905D39A041E: message-id=<744A7ED15EAB1447B0011004ED33376501296912@HIDDEN>

Jan 16 10:59:53 smtp postfix/qmgr[298]: B905D39A041E: from=<HIDDEN>, size=161277, nrcpt=2 (queue active)

Jan 16 10:59:53 smtp postfix/smtp[21010]: B905D39A041E: to=<HID...@cbhc.uk.com>, relay=none, delay=1.2, delays=1.2/0/0.05/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=cbhc.uk.com type=A: Host not found)

Jan 16 10:59:53 smtp postfix/smtp[21010]: B905D39A041E: to=<HID...@cbhc.uk.com>, relay=none, delay=1.2, delays=1.2/0/0.05/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=cbhc.uk.com type=A: Host not found)

Jan 16 10:59:53 smtp postfix/bounce[21013]: B905D39A041E: sender non-delivery notification: F185D51A005F

Jan 16 10:59:53 smtp postfix/qmgr[298]: B905D39A041E: removed

Postconf -n Output:

config_directory = /etc/postfix
delay_warning_time = 4h
disable_vrfy_command = yes
local_recipient_maps =
local_transport = error:local mail delivery is disabled
mail_name = Ontraq
message_size_limit = 20480000
mydestination =
myhostname = smtp.ontraq.com
mynetworks =
myorigin = ontraq.com
smtpd_recipient_restrictions = permit_sasl_authenticated reject
smtpd_sasl_auth_enable = yes
smtpd_sasl_path = private/auth
smtpd_sasl_security_options = noanonymous noplaintext
smtpd_sasl_tls_security_options = noanonymous
smtpd_sasl_type = dovecot
smtpd_sender_login_maps = hash:/etc/postfix/relay_domains
smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/sender_access reject_sender_login_mismatch
smtpd_tls_auth_only = yes
smtpd_tls_cert_file = /etc/postfix/smtp.ontraq.com.pem
smtpd_tls_key_file = /etc/postfix/smtp.ontraq.com.key
smtpd_tls_loglevel = 0
smtpd_tls_security_level = encrypt

Kind regards,

James Day

ko...@jromiak.com.ar

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Jan 16, 2014, 7:13:34 AM1/16/14

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El 16/01/2014 08:52 a.m., James Day escribió:
> Hello Postfix User List,
>

> I'm struggling to work out why postfix is unable to forward
> this message when there is a valid MX record.

It is *not* Postfix problem, but solely DNS problem.

cbhc.uk.com uses 2 DNS servers: NS1.NSNOC.COM and NS2.NSNOC.COM
The problem is that NS2.NSNOC.COM responds to queries about
cbhc.uk.com, while NS1.NSNOC.COM doesn't.

> The error states that there is no A record for the domain name
> (which is correct) but I would have thought Postfix should be
> looking for an MX record as well.

Postfix searches for MX records 1st, then for A. But apparently
NS1.NSNOC.COM (bad luck!) was queried. and NS1.NSNOC.COM said that
there's not MX record, well, then Postfix tried to find A record,
as should, but A record doesn't exist too... (as thinks NS1.NSNOC.COM).

Advise cbhc.uk.com to fix their DNS, NS1.NSNOC.COM and
NS2.NSNOC.COM *must* have the same data. Or you'll see
random troubles: sometimes mail works, sometimes doesn't, depends
on which of 2 DNS servers was queried. And remember about cached
and reused DNS data...

Regards.

Robert Schetterer

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Jan 16, 2014, 7:16:59 AM1/16/14

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Am 16.01.2014 13:13, schrieb ko...@jromiak.com.ar:
> El 16/01/2014 08:52 a.m., James Day escribi�:

after all dont use 8.8.8.8 in mailservers, you might fail with rbl
lookups ( if you like to use that ), use some dns caching only software
with your upstream dns server etc

Best Regards
MfG Robert Schetterer

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martijn.list

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Jan 16, 2014, 7:17:28 AM1/16/14

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On 01/16/2014 12:52 PM, James Day wrote:
> Hello Postfix User List,
>

> I have a mail server that I use to provide a smart host service for my customers. I have a problem sending a message onto a recipient in the domain cbhc.uk.com. The failure message is below.
>

> I'm struggling to work out why postfix is unable to forward this message when there is a valid MX record.
>

> The error states that there is no A record for the domain name (which is correct) but I would have thought Postfix should be looking for an MX record as well.

There must be something wrong with one of your DNS servers. About half
of the DNS requests for the mx record return NXDOMAIN (i.e.,
Non-Existent Domain).

Kind regards,

Martijn Brinkers

--
DJIGZO email encryption

James Day

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Jan 16, 2014, 7:20:50 AM1/16/14

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Thank you everyone for your prompt responses.

Just bad luck on my part that my dig returned records from the mail server that has MX records and postfix queried the other.

I will contact the recipient domain and inform them of the issue.

Kind regards,

James Day