SPF for dummies
Basically, the two direct benefits of SPF i found are :
- ensuring a spammer/virus/trojan cannot send emails using your email address in the FROM field of the email.
- get legitimate emails to go through hotmail (and others of course) junk filter, and not be detected as spam.
I would describe SPF as a process by which a mailserver, when receiving an email with a "From field" indicating a domain hosted on your servers, can check that the mail server that did send the emails is listed as a legitimate server by the domain's DNS manager (you i suppose). He does so by requesting the SPF record of the email from field domain name.
The originating domain mail server will then reply either with:
- yes, it is valid (mail server is listed in my allowed mailservers ip addresses);
- no, it is not valid (mailserver not listed in my allowed mail servers ip addresses);
- failed = no spf record available
- dunno = spf record does not give an exclusive list of mailservers.
Microsoft did a SPF wizard that i found much better than the one listed above:
http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/default.aspx
Now, attention please: when creating your SPF record, list your allowed mailservers (possibly mail.<domain>) but don't forget your users might be accessing the internet with an ISP obligating them to use the ISP's SMTP servers. (This is for example the case here in belgium with skynet - we have to use relay.skynet.be as SMTP server).
So these need to be listed too in the allowed servers. I'm not 100% sure of this but it seems logical to me. Can someone confirm this?
i hope this helps a bit,
Alex