SPF -all

For those system administrators that make settings of their Sender Policy Framework (SPF) with –all in their DNS zone records, I like to pay my tribute to them. They are the real anti-spam heros that have the competent knowledge to fight against spam.

What does SPF –all mean ?

"v=spf1 ip4:1.2.3.4 -all"

In the first line, it tells only the IP address 1.2.3.4 can claim to use the designated domain name in "mail from" field. All other IP addresses can never claim.

v=spf1 a:mail.example.com a:xyz.example.com -all"

Similarly, in the second line above, two hosts can claim to use the designated domain name in the "mail from" field while all others will be rejected.

Sadly, only about 1 % of domain names in use are having SPF -all settings in place.