Tämä on vanha versio dokumentista!
DMARC and SPF break many long-time common email usage patterns like forwarding and mailing lists.
If you set up DMARC with ”reject” you're in effect saying you don't want email from you to be delivered reliably. Same is true for dropping incoming messages based on DMARC or SPF alone, you're saying you don't want your users to receive some of their real emails.
Email is valuable because the user is in control, and these methods try to restrict what the user can do and lock-in the user to their ISP email account.
The value of DMARC and SPF in fighting spam and domain misuse is also very limited and short lived, as the spammers very quickly adapt, so the end result is just to break email for many users without getting much in return.
Please look at DKIM and better multi-method email filtering solutions instead.
More information (in Finnish) at