Hello,

I have a few domains using my mail server: mail.mydomain.com
in the DNS record of mydomain.com, I have the following SPF records:

mydomain.com. IN TXT "v=spf1 mx -all"
mydomain.com. IN TXT "v=spf1 a -all"
mail.mydomain.com. IN TXT "v=spf1 a -all"
mail.mydomain.com. IN TXT "v=spf1 mx -all"

However I still reveive spam emails with the adress user@mail.mydomain.com

Can anybody help?

Regards,

macadam

I don't think you understand SPF correctly. SPF is designed as an "authentication" mechanism for mail servers to validate that a particular piece of mail is coming from a legitimate mail server for a given domain.

The records you have added allow other mail servers to validate your domain. These records don't do anything for your domain. SPF also won't do anything unless you have an SMTP server that has implemented SPF. Furthermore, SPF simply blocks spam coming from hosts that it cannot validate as legitimate mail servers for the sending domain. It does nothing to block spam coming from legit mail servers based on content of the message.

Finally, using SPF at this point would likely block email from literally *millions* of domains. If implemented correctly, an SPF-enabled SMTP server would drop mail for which it cannot validate any mail servers. So if a given domain does not have a valid SPF record, the message would be dropped. The SPF website "brags" about "tens of thousands of domains" using SPF already. While this may sound like a lot, that number is inconsequential considering that there are something like 25 *million* domains registered under .com alone.

Track, I agree with you totally, but just wanted to mention one thing... counting the number of domains using SPF is a foolish way to judge how widespread SPF has become. It's possible for one server to have thousands of domains. So if that server is mine, I can setup SPF checking on my server and *boom* you now have thousands of domains using SPF.

I read somewhere (I believe spamhaus.com) that they estimate there is something like 100,000 email servers worldwide that is handling the bulk of internet mail.

My understanding of SPF is really limited, but from what I remember, it's
pretty much dead in the water and mostly problematic. Here's a good
read on it:
http://homepages.tesco.net/~J.deBoyn...s-harmful.html

ehhh... servers != domains... and I said domains, so I'm not sure where this is going?