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Email Server Setup Problems

Posted on 2011-03-16
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Last Modified: 2013-11-10
We run a web and email hosting service for small businesses in the area. One of our customers is complaining of undelivered emails from certain domains (linkedin.com, dyndns.com, salesforce.com). Our server hosts multiple domains, including our own. I tested that the domains in question could email our server by signing for accounts myself and receiving the confirmation emails. Everything worked correctly. There is no entry in /var/log/maillog for the emails in question.

Why would these emails be delivered to one account (hockson.com) on a server, but not another account (castillolanguageservices.com)? Hockson.com is the primary domain for the server.

I also have a message in the mail queue stating that a server configuration error occurred (4.3.5). I am using Postfix 2.6.5 on Fedora 12. The needed firewall ports are open (ie: 25 plus the ports for POP and IMAP).
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Question by:tysonk
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by:de2Zotjes
de2Zotjes earned 500 total points
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The most likely explanation (with the info provided) is that the name resolving of the MX record for the 2 domains is different. That checks out when I dig the domains:

~$ dig MX castillolanguageservices.com

; <<>> DiG 9.7.1-P2 <<>> MX castillolanguageservices.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 7230
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 0

;; QUESTION SECTION:
;castillolanguageservices.com.	IN	MX

;; ANSWER SECTION:
castillolanguageservices.com. 300 IN	MX	0 69.57.170.228.

~$ dig MX hockson.com

; <<>> DiG 9.7.1-P2 <<>> MX hockson.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32198
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 0

;; QUESTION SECTION:
;hockson.com.			IN	MX

;; ANSWER SECTION:
hockson.com.		3600	IN	MX	0 smtp.hockson.com.

~$ dig smtp.hockson.com

; <<>> DiG 9.7.1-P2 <<>> smtp.hockson.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47527
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0

;; QUESTION SECTION:
;smtp.hockson.com.		IN	A

;; ANSWER SECTION:
smtp.hockson.com.	3600	IN	CNAME	hockson.com.
hockson.com.		1800	IN	A	69.57.170.228

~$ dig -x 69.57.170.228

; <<>> DiG 9.7.1-P2 <<>> -x 69.57.170.228
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4971
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 1

;; QUESTION SECTION:
;228.170.57.69.in-addr.arpa.	IN	PTR

;; ANSWER SECTION:
228.170.57.69.in-addr.arpa. 86400 IN	PTR	webhost.hockson.com.

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Perhaps the mentioned mail senders will not forward to places where the reverse record points to another domain?

Your mail queue is concerned with mail you are forwarding through this box, so unless it concerns a mail addressed to the bad domain it is probably not related. If it is for the non functioning domain, could you please post the entire message here?

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by:tysonk
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I have completed further testing on this issue and have been able to get email from DynDNS.com to come through castillolanguageservices.com. However, I am still unable to receive mail from LinkedIn.com. I can receive mail from LinkedIn at Hockson.com, but not castillolanguageservices.com. I managed this by altering the smtpd_recipient_restrictions configuration item to permit_mynetworks, reject_unath_pipelining, permit_auth_destination.

Commenting on your suggestion:
I'm not sure I understand what you mean when you say the name resolving is different. Doesn't your output show the same IP for both domains? Shouldn't this pointed to the same server then? If so, why is that it can find the server for one domain, but not the other?
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by:tysonk
Comment Utility
Also...there is no traffic in the logs, nor any postmaster notice generated, for the missing emails.
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Accepted Solution

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de2Zotjes earned 500 total points
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The name resolving is different because the way you get to an ip address is different. Another difference is that the reverse resolving will yield an address in the hockson.com domain.

As for no traffic in the logs, that is an indication the sender machines are unwilling to deliver mail to your box.

Afaik the correct content for an MX record is the name of the machine accepting mail for that entity, so perhaps you should try changing the MX for castillo...com:
castillolanguageservices.com MX webhost.hockson.com.

The downside of playing with dns is that it takes a long time to propagate through the world. Have you contacted the postmaster at linkedin.com with the question? That might yield more insight into what is going on.

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Author Comment

by:tysonk
Comment Utility
So...the MX record for castillolanguageservices.com should be smtp.hockson.com or webhost.hockson.com??
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Author Comment

by:tysonk
Comment Utility
I got it. Set all MX records to smtp.hockson.com. Thank you sooooo much for you assistance.
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