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Linux Tutorial :: View topic - Postfix - Multiple domains and Reverse IP Records
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Postfix - Multiple domains and Reverse IP Records

 
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Lanman
Newbie


Joined: Apr 02, 2006
Posts: 2

PostPosted: Sun Apr 02, 2006 4:48 pm    Post subject: Postfix - Multiple domains and Reverse IP Records Reply with quote

I have a question which relates to DNS configurations.

When a single domain is setup, it's necessary to contact your ISP and have them register the 'Reverse IP Pointer" so that email servers can do reverse lookups and confirm the authenticity of the domain sending emails.

But, how do I configure the Reverse IP record when hosting multiple domains? Do I need separate IP addresses for each additional domain? Or can I configure the Reverse IP Lookup for all other domains on my server by pointing them to a specific record held by the primary (TLD) domain on my server? If that is the case, could someone explain how to accomplish this?

If (for example) I already have "domain1.com" and I want to add "other_domain.com" to the same server and I also want to have separate email capability for each domain (much like a hosting company might have), how would I go about setting up the reverse IP lookups for each, and for that matter, what is needed in order to re-configure Postfix to get this working?

I'm looking to add a few of my own domains to my server and would appreciate any help this forum can offer.

Thanks In Advance,

Lanman
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koen
Beginner


Joined: Sep 12, 2005
Posts: 224
Location: Belgium

PostPosted: Sun Apr 02, 2006 10:21 pm    Post subject: Reply with quote

You can not have multiple PTR records with identical IP addresses, so I see your problem.
However, I've read that this reverse DNS lookup that e-mail servers perform, only checks that a [i.e. any] PTR record exists for the sending mail server - it does not have to match. The assumption is that spamming servers don't have pointer records, either because they use dynamic addresses (and ISP's don't set PTR's for them) or because the spammer doesn't want reverse lookups to reveil a domain name.
So you could try to get away with just 1 PTR.

If that doesn't work, you could try something creative using NAT (network address translation), and use the NATed addresses in PTR records.

You should also look into SPF ([url]http://www.openspf.org/[/url]) : These are special DNS records that indicate for which domein[b]s[/b] a mail server is serving mail, or which server[b]s[/b] are legitimate senders for a given domain.
SPF [b][i]does[/i][/b] check domains against IP addresses, but if I understand it correctly, it works from the forward lookup zone, so with 2 or more domains, you'll have a corresponding number of forward lookup zone files, each of which kan have SPF records.

As for how to configure Postfix, I have no idea.
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Lanman
Newbie


Joined: Apr 02, 2006
Posts: 2

PostPosted: Mon Apr 03, 2006 6:17 am    Post subject: Postfix - Multiple domains and Reverse IP Records Reply with quote

Thanks. I'll look into your suggestions.

Lanman
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jimmo
Administrator


Joined: Jul 27, 2002
Posts: 309
Location: Coburg, Germany

PostPosted: Fri Apr 07, 2006 8:20 am    Post subject: Reply with quote

Perhaps your provider allows you to forward email through them. Both my ISP and web hoster (different companies) allow this. I have configured postfix to authenticate itself with their SMTP server and then they forward my messages. Since I authenticate myself when I connect, they accept the message and forward it. For the most part, that's all that the next hop needs. Since they can completely authenticate my ISP (for example) and my ISP has authenticated me, the message is accepted.

For the details on configuring postfix, start here:
http://www.postfix.org/VIRTUAL_README.html
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