DomainKey signing isn't working. DKIM support is also installed and configured.
DKIM and DomainKeys interoperability conflict occurred because of both DKIM and DomainKeys were configured to use the same
default selector, but crypto keys for these two systems are differ.
Changes should be made on DKIM side.
- Change DKIM selector from
defaultto something else, for example,
- Add corresponding
mail._domainkey.domain.tld.) in Plesk for
- Wait for 'Propagation period'
Note: DKIM is not supported in Plesk 12.5 and earlier. DKIM support in Plesk announced since Plesk Onyx. Implementation details available here