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I've created an SPF record on 123-Reg, which is working great. But my question is how Exchange servers know that an SPF record exists when they receive mail from a domain. How does Exchange know it needs to check the domain's DNS provider, 123-Reg in this instance, for a SPF record, in order to check the mail has come from an allowed sender/IP?


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3 Answers 3

The author of the MTA (in this case Exchange) reads and complies with RFC 4408 and friends.

If everyone does everything right (you publish a proper SPF (TXT) record, the MTA retrieves and interprets it per the RFCs) things Just Work. If someone screws up their part of the deal things break.
(Ain't the internet a grand place?)

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So does Exchange 2010 require any specific modifications in order to know to look for an SPF record? – PnP Sep 14 '12 at 19:41

when a Mailserver (Exchange) with SPAM detection and SPF validation receives a Mail from a Server IP with Sender Domain he will check if the Domain has an MX Record for the Server when not the Mailserver will check the SPF Record. If the Server IP or Network is in the SPF Record the Mailserver will receive the Mail. So with SPF you allow Mailservers to send Mails from a Domain where they are not in the MX Reocords

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Mind using some Markdown formatting and standard English grammar so this is readable? It's a sea of random capitalization right now, and it makes my brain hurt :-) – voretaq7 Sep 14 '12 at 20:20

Exchange "knows" to do this if you have it configured to do this.

In Exchange Server 2003 you configure Sender ID filtering in GlobalSettings|Message Delivery and then enable it on the SMTP Virtual Server.

In Exchange Server 2007 and 2010 you enable and configure it on your Edge Transport server. If you don't have an Edge Transport server you can enable it on your Hub Transport server.

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Whereabouts in Hub Transport must I configure it? – PnP Sep 14 '12 at 19:38

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