Mail server ptr record

i have a mail server in my company, i'm using linux, sendmail and bind i have it installed on the same server. i have 2 domains on the same server  x.com and y.com, i have my isp ptr record pointing to mail.x.com and mail.y.com, for some reason i can't send emails from mail.x.com to some domains that check ptr records, but i can with mail.y.com. my question is how do i need to setup my mail exchanger because i think is the order of my ptr records and those servers are pulling the first record, i did some read about it, and it is recommended to have just one ptr record, but how do i setup my 2 email domains over the same server and same ip? please help!!!
DoradoITTeamAsked:
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feptiasCommented:
You should have the MX records for both domains - x and y - pointing to a single mail server host record. Then there will only be a need for one PTR record matching the single mail server host record.

Then check that your DNS is set correctly by running reports for each domain using this link:
http://www.dnsreport.com/
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DoradoITTeamAuthor Commented:
Do i need to change my server hostaname? or just create my mx exchanger and point the 2 domains on the same server..
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feptiasCommented:
It depends if the server hostname is used in the SMTP header when you send mail. This can be easily checked by sending an e-mail from an account in domain x or y to an external account. After it has been received it should be easy to view the headers although the exact method for doing so depends on the e-mail client: In MS Outlook you can right-click on an e-mail in the Inbox and select Properties (Outlook Express) or Options (Office Outlook). You need to look for the section that says "Received: from ....." within the headers.

Once you have established what name and IP address is shown for your mail server in the headers, then you need to ensure that the Internet DNS for that name and that IP address are configured correctly. If the name appearing in the headers is not the one you want to use then changing the server hostname may be one way to change it. My expertise is more in Windows than Linux - I know that MS Exchange allows you to set the mail server name that appears in the headers to something different to the actual server hostname. Your mail server may also allow this.

To be able to send mail to those domains that check ptr, you need your public DNS records configured as follows:
A forward lookup on the server name shown in the header must return the IP address shown in the header
A reverse lookup (using the PTR record) on the IP address shown in the header must return the server name shown in the header.

While you are looking at this subject, I recommend you also take a look at SPF. It is another mechanism that helps prevent spoofing of mail server names by spammers. Here are some links:
http://www.openspf.org/Introduction
http://en.wikipedia.org/wiki/Sender_Policy_Framework
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