"v=spf1 -all"

In SPF, the setting of "v=spf1 -all" is interesting. I have found one domain to illustrate:

[root@~]# host -t txt wa-first.com
wa-first.com descriptive text "v=spf1 -all"
[root@~]#

That say, no domain or IP address can claim to use the domain wa-first.com in the "mail from" field of email address. If the domain is used for hosting web only and no email is involved, this is a proper setting with great protection.