Sendmail - Unable to send External mails to one particular domain

[Bejoy C Alias]

Hi guys
The pblm is like this.
We had registered our domain centuryenka.com and hosted our web and mail server and Primary/secondary domain servers for this domain are also in our premises . We are able to send mails to other domains like yahoo.com rediffmail.com hotmail.com etc .. from this mail server directly except the domains in vsnl ( like vsnl.com vsnl.net etc. ) . We are getting the failure reason as "Deferred: 450 4.1.8 invalid/host-not-in-DNS return address not allowed" to the reply to Mail from :hcl@centuryenka.com. But when we do a domain lookup ( dig ) for the centuryenka.com we are able to resolve everything including the MX records and NS records . But unable to reverse lookup our mail server ip on other DNS servers . Whether this is because of any spam prevention rules implemented in vsnl's servers to block mails from ips that is not having valid reverse lookup answer ?. OR any DNS configuration issues in our DNS servers. Pls guide us to solve this pblm.

With Advance Thanks and Best Regards
Bejoy C Alias

[Mic V.]

Bejoy,

I haven't dealt with DNS in a while and I'm just going by memory -- haven't looked into your specific DNS.

Since you say you can't do a reverse lookup, I was reminded of a problem at my last company. The registrar we used did not provide reverse lookup capability for its clients.

Hope this provides a clue.

Mic

[Vitaly Karasik_1]

You should ask your provider [owner of this network range] to add reverse DNS record for your mailserver.

[Bejoy C Alias]

Ok guys,
let us speak with our isp regarding the reverse lookup entry

will be back.

[Bejoy C Alias]

Hi..i'm back
the reverse lookup entries are created on the isp's servers and i am able to reverse lookup my server ip from other isp's dailup connections also. But the problem of sending mails to vsnl.com users is still existing. I found that some of other servers ( like itgi.co.in ) are not able to resolve the domain centuryenka.com because of this i'm not able to send mails to this domain also .If we use the vsnl's webmail through internet , iam able to send mails to our domain, but using outlook express which is configured with vsnl's user id and smtp server we are not able to send mails to our domain it is giving bounce back as mx record not found after one day . We are using a 64kbps leased line for this dns servers and webserver. Is this because of this connection speed that the external users are not able to contact our servers at time. Or any config issue with the dns servers.

awaiting for ur reply...

[Vitaly Karasik_1 · Accepted solution]

Bejoy ,

You may check your DNS configuration online using http://www.dnsstuff.com, for example.
And, as far as I see, there are a problem -
your DNS server answers only after several errors.

Regarding reverse [PTR] records - what is your *outgoing* mail server? - you should add PTR record for such server.

[Steven E. Protter]

Are your reverse lookup records for the ip addresses being used to send mail set up.

My mail servers are set up to reject any mail from smtp clients that do not have valid reverse lookup records. This was done to cut down on spam, based on log analysis.

Diagnosis tools:

sendmail -v -d8 -d38 someone@networkwithproblem.com

type some text

.


You will probably get a similar error, but some of the text you get back may confirm my conclusion.

This problem is fixed by setting up valid reverse DNS records.

Also, its possible the prior owner of your ip address was an open relay server or spammer. That may have gotten the numeric ip address denied.

SEP

[Bejoy C Alias]

Hi..
iam able to reverse lookup the out going mail server's ip address from other dns servers. is there any pblm with the link speed which iam using for our web/mail server b'coz of which the other servers are getting time outs . we are using a 64kbps ( 1:1 ) link for our mail/dns/web servers.
my server's ip address is not listed in any spam databases , so that won't be a pblm. so the issue may be with link speed.

[Vitaly Karasik_1]

Bejoy, can you please sned me email to

vitaly_il at yahoo dot com

?

Rgds,
Vitaly

[Bejoy C Alias]

Hi Guys...
Finally my pblm got solved.
It was a firewall configuration issue on the second dns server, b'coz of which the vsnl's servers were not able to resolve centuryenka.com ( they might have used my secondary dns server for looking up centuryenka.com all the time , but it was not answering anything to outside world ). After making it online to the outside net my mail server started sending mails to vsnl's server and i can receive mails from vsnl's domain .

Specific thanks to Vitaly Karasik for noticing me about the errors u got from dnsstuff.com and helping me to resolve the issue by using your refered site .

Thanks to Steven & Mic for their valuable replys ..