* update SPF record: replace protonmail with poste.io mail server
PESO-77
- replace include:_spf.protonmail.ch with ip4:167.235.134.154 and ip6:2a01:4f8:1c1e:9c53::1 (nuremberg-a / mail.pez.sh)
- tighten from ~all (softfail) to -all (hardfail)
* tighten DMARC policy from p=none to p=quarantine
PESO-78
- enforce DMARC with p=quarantine (failed messages get quarantined)
- add adkim=r and aspf=r for relaxed DKIM/SPF alignment