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Postfix : Host Not found

Posted on 2012-04-07
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Last Modified: 2012-04-08
Action: failed
Status: 5.4.4
Diagnostic-Code: X-Postfix; Host or domain name not found. Name service error
    for name=mail.mydomain.com type=A: Host not found


Above is what I get when I send email to New Postfix Server.

(Host Name and Domain Name is correctly set +mxtoolbox complains for reverse DNS ).

I need to fix it ASAP. Please help.
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Question by:amit_panjwani
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by:arnold
arnold earned 250 total points
ID: 37821198
Look whether locally that name resolves as well.
The problem s that the entry does not seem as coming from postfix.
nslookup mail.mydomain.com

Do you have local dns for mydomain.com while it is also dns served externally?
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Papertrip earned 250 total points
ID: 37821232
Also contact your ISP and have them create a PTR record for your sending IP which matches the A record.
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by:amit_panjwani
ID: 37821492
@arnold - when I do nslookup - I get a list of name servers for this mail server. That should be ok.


@ papertrip - I believe thats some thing already done - anything diagnostics that can verify that
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by:arnold
ID: 37821590
No, that is the problem. The local dns server must resolve the ip rather than refer the application to another source of information.
You can configure your local name server to resolve for local subnets.
Once you correct this, you should not have this issue.
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by:Papertrip
ID: 37821681
You said initially that mxtoolbox said reverse did not match.  If you want to check from another external source then just put your sending IP into http://network-tools.com/ and make sure it resolves to whatever the A record is for your sending server.
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by:amit_panjwani
ID: 37821702
Allow me to compound this problem :(

I was running sendmail earlier on same server - (Same DNS settings). I was able to receive emails from Gmail and yahoo - No issues.

I was able to send emails (External mail relay)

AFTER - Switching to Postfix :

Now - I can send mails (External relay server). But I cannot receive any emails. Thats the point where I get this error : Host not found.

Please help
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by:arnold
ID: 37821728
The error than is not from postfix but from exchange?
You have to be on the system that generates the email and check its configuration.
Try to cobble together information will lead to unrelated suggestion that could make matters worse.  Run lsof -i:25 where postfix is installed an see what is being reported.
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by:amit_panjwani
ID: 37821750
@arnold I know what you are trying to suggest . I had already uninstalled sendmail - before I pushed for Postfix.

I think I have resolution. It was all ISP issue -  Static IP resolves bit differently.

I have raised ticket and they are going to resolve it in next 6 hours.

Thank you!
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