DNS and postfix mail

brakethrew
brakethrew used Ask the Experts™
on
Hello all

I have 2 linux servers one is the gateway - squid - mail - firewall the other is the DNS - Application - Fileserver. recently the Fileserver crashed and had to be rebuilt and reloaded from backup. I used a new OS (Fedora11) and it is all up and running - after rebuilding the DNS I am having a problem with sending Emails, mails are being bouced back Immediately with the error

Host or domain name not found. Name service error for
    name=xxxx.com type=A: Host found but no data record of requested type

when we send the mail again MOST times the mail shoots through sometimes we need to send it a few times

I know it has something to do with postfix checking DNS have searched but to no avail...

can anyone help please?
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David BeveridgeLinux Systems Admin

Commented:
How many name servers do you have listed in /etc/resolv.conf?
Try adding
nameserver 8.8.8.8

Author

Commented:
hi bevhost

My resolv.conf has my internal caching DNS and then the 2 isp DNS's

domain xxxx.co.za
nameserver 10.20.0.245
nameserver x.x.x.x
nameserver x.x.x.x

hope this helps
peter

Author

Commented:
OK added 8.8.8.8 as one of the nameservers in resolv.conf just testing right now

does it matter in which order the nameservers are placed?
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Author

Commented:
tested with 8.8.8.8 in resolv.conf random mails still bounce back

anybody have any suggestions?
David BeveridgeLinux Systems Admin

Commented:
The domain xxxx.com in your question, is that local or remote?
David BeveridgeLinux Systems Admin

Commented:
When you do a dns lookup for xxxx.com is there an MX record or an A record?

eg
When I try it here I get this...

# host xxxx.com
xxxx.com has address 209.85.112.193
xxxx.com mail is handled by 10 mail.xxxx.com.
David BeveridgeLinux Systems Admin

Commented:
If the DNS it really flaky to that address you can route that domain specifically to an IP address in /etc/postfix/transport

xxxx.com     smtp:[98.76.65.43]

Author

Commented:
Hi Bevhost

sorry for the late reply

the domain in question is my local domain.

if I do a dig of google.com here is the result

#dig www.google.com

; <<>> DiG 9.3.4-P1.1 <<>> www.google.com
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35534
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 4, ADDITIONAL: 0

;; QUESTION SECTION:
;www.google.com.                        IN      A

;; ANSWER SECTION:
www.google.com.         583274  IN      CNAME   www.l.google.com.
www.l.google.com.       51      IN      A       72.14.203.104
www.l.google.com.       51      IN      A       72.14.203.105
www.l.google.com.       51      IN      A       72.14.203.106
www.l.google.com.       51      IN      A       72.14.203.147
www.l.google.com.       51      IN      A       72.14.203.99
www.l.google.com.       51      IN      A       72.14.203.103

;; AUTHORITY SECTION:
google.com.             151270  IN      NS      ns4.google.com.
google.com.             151270  IN      NS      ns2.google.com.
google.com.             151270  IN      NS      ns1.google.com.
google.com.             151270  IN      NS      ns3.google.com.

;; Query time: 1 msec
;; SERVER: 10.20.0.245#53(10.20.0.245)
;; WHEN: Mon Feb  1 15:11:04 2010
;; MSG SIZE  rcvd: 220

also the mail is not only bouncing to ONE specific address it is bouncing when sending to any address, and then sends it when you try again the second or third time -  but then again sometimes it DOES NOT bounce at all and just goes through.

kinda confusing and also takes a while to test.

Author

Commented:
as regards the host command

if I do a # host google.com it does give me the mail host as well

# host google.com
google.com has address 72.14.203.99
google.com has address 72.14.203.103
google.com has address 72.14.203.104
google.com has address 72.14.203.105
google.com has address 72.14.203.106
google.com has address 72.14.203.147
google.com mail is handled by 10 google.com.s9b2.psmtp.com.
google.com mail is handled by 10 google.com.s9a1.psmtp.com.
google.com mail is handled by 10 google.com.s9a2.psmtp.com.
google.com mail is handled by 10 google.com.s9b1.psmtp.com.

Author

Commented:
has this question just been dropped, is there anyone out there that can advise me - please
David BeveridgeLinux Systems Admin

Commented:
You really haven't given us much to go one here,
Are you sending mail to xxxx.com or from xxxx.com
Are the xxxx.com mailboxes on the postfix server?


The actual error message means that the server (postfix) tried to look up the A record for xxxx.com, found the domain exists, but no A record.

It could be looking for an A record because no MX record exists.

Your results could vary from time to time depending on whether the answer comes from your internal caching server OR from one of those external servers.

If it is an internal domain, it should be configured to operate without the assistance of DNS
OR you internal DNS needs to work properly.

Are you getting any other error messages?

Author

Commented:
Hi Bevhost

xxx.co.za is MY domain I am trying to send out from xxx.com, the mail bounces back to the sender saying so I am sending from xxx.co.za

Host or domain name not found. Name service
    error for name=za.endress.com type=A: Host found but no data record of
    requested type

as mentioned above but not every time, only one in 7 mails - when we resend the same mail it normally goes the second or third time.

I was just hoping that someone has come across this error, and perhaps I have messed up a setting in the caching DNS that I newly setup. and the fact that the error is random makes it hard to troubleshoot.

/var/log/mail.warn gives errors like this

Feb  5 12:27:32 gateway postfix/smtpd[8862]: warning: 117.6.2.232: address not listed for hostname cfc.com.vn
Feb  5 12:31:02 gateway postfix/smtpd[10603]: warning: 122.168.245.204: hostname ABTS-mp-dynamic-204.245.168.122.airtelbroadband.in verification failed: No address associated with hostname

no other logs relating to mail show anything related to hosts or domain

hope this helps



David BeveridgeLinux Systems Admin

Commented:
Try removing all the nameservers from resolv.conf except your local one and see what happens.

Author

Commented:
ok will do

Author

Commented:
when I take out all the other nameservers I seem to get more bouncing.
question, does a caching dns server learn and store DNS information and could it be that the reply for host lookup takes a little while - and if so is there anyway I can slow down the bounceback or the time it takes for postfix to do a DNS lookup of the domain? if you understand what I am getting at.

Author

Commented:
sometimes when I do a #host command on any arb domain I get a
;; connection timed out; no servers could be reached and then second time it works

It is definitely a DNS issue and I am not sure what I have done wrong - I created the new DNS using the following set up

http://tldp.org/HOWTO/DNS-HOWTO-3.html

maybe I made a mistake
David BeveridgeLinux Systems Admin

Commented:
That list of root servers looks a bit out of date
I have these in my DNS server

;; ADDITIONAL SECTION:
A.ROOT-SERVERS.NET.     3600000 IN      A       198.41.0.4
A.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:503:ba3e::2:30
B.ROOT-SERVERS.NET.     3600000 IN      A       192.228.79.201
C.ROOT-SERVERS.NET.     3600000 IN      A       192.33.4.12
D.ROOT-SERVERS.NET.     3600000 IN      A       128.8.10.90
E.ROOT-SERVERS.NET.     3600000 IN      A       192.203.230.10
F.ROOT-SERVERS.NET.     3600000 IN      A       192.5.5.241
F.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:500:2f::f
G.ROOT-SERVERS.NET.     3600000 IN      A       192.112.36.4
H.ROOT-SERVERS.NET.     3600000 IN      A       128.63.2.53
H.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:500:1::803f:235
I.ROOT-SERVERS.NET.     3600000 IN      A       192.36.148.17
J.ROOT-SERVERS.NET.     3600000 IN      A       192.58.128.30
J.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:503:c27::2:30
K.ROOT-SERVERS.NET.     3600000 IN      A       193.0.14.129
K.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:7fd::1
L.ROOT-SERVERS.NET.     3600000 IN      A       199.7.83.42
M.ROOT-SERVERS.NET.     3600000 IN      A       202.12.27.33
M.ROOT-SERVERS.NET.     3600000 IN      AAAA    2001:dc3::35

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Author

Commented:
changed that, still getting bounced mail every so often

Linux Systems Admin
Commented:
Not sure why you followed those instructions for installing DNS.

I would do it like this..

# yum install caching-nameserver
# chkconfig --levels 345 named on
# service named start

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