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Must MX record and PTR record be the same IP address?

Posted on 2006-11-02
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Last Modified: 2008-01-09
Hi I've got 2 scenario.

Scenario 1

One of my clients is hosting their email with a static ip. Some clients are rejecting their mail because they do not have a valid PTR record. I know I got to go thru an ISP to add the PTR record. Which IP should i tell them? Is it the MX record of that mail server or any public IP within the available range of that client? Say the MX record is 203.111.10.10. Must the PTR record be like 203.111.10.10 to mail.abc.com?

Scenario 2

Another client of mine is not hosting their email but downloading email by Mdaemon throught POP. Their outgoing mails are sent out by Mdaemon directly. If this is the case, shall i apply their PTR record to be one of my client's public ip address?
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Question by:totallypatrick
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17 Comments
 
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Assisted Solution

by:arnold
arnold earned 900 total points
ID: 17864871
Scenario 1: the PTR record that matches the IP from which the mail is seen (the IP mail server) is the one that needs to be updated.  The MX record can not and should not point to an IP but to a hostname.  The IP of the Hostname needs to be updated as a PTR record as the hostname.

Scenario 2:  If mdaemon has the option, you should configure it to send the email back through the ISP's mail servers and not attempt direct delivery since that could run into a situation that the mail is rejected.

A PTR record can only be setup for an IP address to reflect a Host record (A record)
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Expert Comment

by:Busbar
ID: 17865005
Scenario 1:yes it should be
Scenario 2: just as arnold said
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Expert Comment

by:MarkWYnne
ID: 17865670
as above

PTRs (Pointers) are reverse lookups matching one to several IPs to one name. MX (Mail xchange)
records do as they say on the tin, facilitate exchange mail between domains.


Try > nslookup > set q=mx > anydomain.com to verify mail servers, this will tel you where mail will end up for a specified NS name.

..


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Assisted Solution

by:greggers8086
greggers8086 earned 300 total points
ID: 17865703
your ISP should have already set you up a PTR record

you can check the PTR record for your domain using nslookup from the command prompt
type nslookup
at the ns lookup prompt type "set type=ptr"
then type the ip address

PTR record should read something like 0.10.111.203.in-addr.btopenworld.com if your isp is bt

you can change the dns server that you are querying using the server command.

Generally you set up a cname for mail.yourdomain.com then set mx1 to be mail.yourdomain.com  this is considered good practice.

you can also check your mx using nslookup and set type=mx

I've never ever had to set-up a PTR record so I'd be very supprised if this is the problem.  Try running some diags with nslookup and post back your findings.
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Author Comment

by:totallypatrick
ID: 17865916
Thanks for all the reply

To arnold

Scenario 1: You're saying set the ptr to where the mail server is seen. My setup is as follows. MX record ip address (smtp port) 203.XX.XX.XX will be forwarded from my firewall to the internal address of the mail server on the local lan which is 192.168.1.X. What then is regarded as the mail address of my mail server? Is it the mx record or the public ip my firewall use for NAT (meaning the ip address that is found from http://whatismyip.com).

Scenario 2: Yes Mdaemon has the option to forward all mails to my isp mail server. We've tried that but it seems that the isp mail server can't take the load of mass mailing or some restriction is applied. It can't send out fast enough and mails keep pilling up in Mdaemon.

"A PTR record can only be setup for an IP address to reflect a Host record (A record)" --> what does this sentence mean? Must I also set up an A record for my domain then for PTR I  apply my host name eg. mail.mydomain.com to that A record IP that I have set up?

To MarkWynne

What do you mean by

PTRs (Pointers) are reverse lookups matching one to several IPs to one name. MX (Mail xchange)
records do as they say on the tin, facilitate exchange mail between domains.

Are you saying a single PTR can match several MX records for a single domain?

To greggers8086

Singapore ISP dun set that up. We've got to apply by filling up a form and submit it :P

Generally you set up a cname for mail.yourdomain.com then set mx1 to be mail.yourdomain.com  this is considered good practice. --> Cname is the same as A record right? So i should apply a host name for my mail server and then set my PTR record to mail.mydomain.com

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Author Comment

by:totallypatrick
ID: 17865985
Is it possible to give me an simple example of what i should do?

A record = mail server hostname ???
MX record = ip address of mail exchange record
PTR record = ???
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Author Comment

by:totallypatrick
ID: 17866051
I give my theory and you guys see whether its right.

1)  I should apply an A record for my Mail server --> mailserver.mydomain.com resolves to 11.22.33.44
2) I should apply MX record required by mail server --> mydomain.com resolves to 11.22.33.44
3) I should then apply for my PTR --> 11.22.33.44 resolve to mailserver.mydomain.com

Everything I use will be the same ip of 11.22.33.44
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Expert Comment

by:MarkWYnne
ID: 17866122
regarding PTRs. If you wish to have your ISP route mail to your domain, they will create a pointer record and add the addresses of your mail server\s. So when mail destined for your domain goes through the ISP's domain, the  pointer will have your server IP\s and DNS will give a name for your mail servers.

PTR Totallypatrick.com
84.203.55.74
84.203.54.74 ect

MX records will have the DNS names of these servers and other information
ie mail1.totallypatrick.com & mail2.totallypatrick.com

MX records ultimately route mail between domains. whereas PTR and A records handle individual resolutions.

I am fairly new to messaging, if anyone thinks I am wrong speak up as I don't want to give wrong infgormation to anybody.
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Expert Comment

by:MarkWYnne
ID: 17866224
Basically... If you send a mail, it goes to your ISPs smtp queue, upon processing the address someone@totallypatrick.com is checked against the mail servers MX record for totallypatrick.com. which is Mail.totallypatrick.com, "the A record will have the IP" once the mail is sent to Mail.totallypatrick.com your exchange environment will resolve the mail to a recipient and deliver it to the mailbox.
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Expert Comment

by:MarkWYnne
ID: 17866234
I meant the pointer will have all IPs for your mail servers,
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Author Comment

by:totallypatrick
ID: 17866272
HHmm ok..to make it simple, this is what i've gathered. Is this following correct?

Step 1:
 
We must always apply an A record for our mail server. This A record will be used as MX record also
 
Example
mailserver.postmark.com.sg resolves to 203.118.31.3
 
Step 2:
 
The MX record will be pointed to this A record of our mailserver instead of an IP address
 
Example
 
postmark.com.sg resolves to mailserver.postmark.com.sg
 
Step 3:
 
We must apply rDNS record to point back to the host address
 
Example
 
203.118.31.3 resolves to mailserver.postmark.com.sg
 
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Expert Comment

by:MarkWYnne
ID: 17866334
Apologies for confusing the issue, noob to xchange and EE.

Thats about the meat of it, ..to add. the pointer PTR will have the IP to name lookup

When creating a PTR you specify the domain and add your valid IP addresses for the corresponding hosts.

Hope this all helps.
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Author Comment

by:totallypatrick
ID: 17866388
Is specifying the domain or the host for PTR? I think it should be the FQDN of the host name right? e.g. xx.xx.xx.xx resolves to smtp1.mydomain.com ??
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Accepted Solution

by:
MarkWYnne earned 300 total points
ID: 17866456
Spot on.. def should be FQDN
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Expert Comment

by:MarkWYnne
ID: 17866473
You want to point it to the host   %host%.mydomain.com
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Author Comment

by:totallypatrick
ID: 17866564
Thanks Mark. I'll ask my isp to set it up on mon
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Expert Comment

by:MarkWYnne
ID: 17866623
No probs m8. Most welcome.
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