- Plesk 12.0 for Windows
- Mails are not signed correctly by DomainKeys
- DNS server is installed and activated for this domain
- Domain DNS zones are hosted by other server
DomainKeys will not work properly as public key for DomainKeys is located on DNS server.
Regrading the DomainKeys there private and public keys might be out of sync which causes that issue. To avoid this please point Plesk DNS in domain registrar settings. Using Plesk DNS is necessary condition according to official documentation .