There is one point about the setup of SPF records in DNS that confuses me: SPF compares the return address of email against the IP of the MX record for that domain. However, the MX record doesn't point to an IP, it points to a host name, which may be in another domain. So the MX record for abc.com may point to mail.xyz.com. So when systems do an SPF lookup, do they just find the IP of mail.xyz.com and use that, and ignore the fact that that mail server really belongs to another domain?
Correct. SPF doesn't care about any domains, except the domain of the sender. So if the sender is [EMAIL PROTECTED], and the MX record for abc.com is mail.xyz.com, then SPF will check to see if the IP address that the E-mail is being sent from is in the A record of mail.xyz.com. In other words, if the E-mail is really being sent from mail.xyz.com, it will pass SPF.
-Scott
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