Overview

Much of this article can be found on http://spf.pobox.com. Have you ever gotten spam from yourself? We have, and we have been thinking hard about how to stop it! We didn't send it. It came from a spammer. If we could stop spammers from forging mail, we could easily tell spam from ham and block the bad stuff. 免费资源www.it55.com

Sender Policy Framework (SPF) makes it easy for a domain, whether it's an ISP, a business, a school or a vanity domain, to say, «I only send mail from these machines. If any other machine claims that I'm sending mail from there, they're lying.» IT资讯之家 www.it55.com

As an example, akadia.com is the sending domain, and arkum.ch is the receiver. Akadia.com publishes an SPF record, specifying which computers on the Internet can send mail as user@akadia.com.

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1. When a real Akadia user sends mail, arkum.ch receives the message from an Akadia server.
    
2. Arkum checks Akadia's SPF record, to make sure the server is allowed to send mail from Akadia.
    
3. If the server is listed, so Arkum gives the message a pass. If the server is not listed, so Arkum gives the message a fail. When a spammer forges mail from Akadia, Arkum receives the messages from an outside server.

DNS Setup (Publishing SPF)

Suppose akadia.com wants to publish SPF, so it adds the following line to its DNS zone file:

vd;k;l www.it55.com rdfg

akadia.com. IN TXT "v=spf1 a mx ptr -all"

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The v=spf1 version string identifies this as an SPF record. The -all means reject all mail by default. Domains that don't send any mail,  can get by with simply v=spf1 -all. But if the domain does send mail, it declares mechanisms that describe how legitimate mail should look. Mechanisms go in the middle, before
 -all. The first mechanism to match provides a result for the SPF query. -all always matches and so belongs at the end.

sflj www.it55.com kg^&fgd

• A: the A mechanism means the IP address of akadia.com is permitted to send mail from akadia.com. If you w sflj www.it55.com kg^&fgd

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