Enable dmarc mitigations

Hello all!

Currently Fedora mailing lists use "From" field from original messages
and if sender's domain use DMARC=reject policy, mailing lists
subscribers cannot receive any messages from such users because their MX
servers follow DMARC procedure and drop them.

Previously I opened ticket in Fedora Infra[1].

Someone need to fix this because more and more mailing servers starts
enforcing DMARC=reject.

[1]: <a href="" title=""></a>