How can I send DMARC-compliant mail? 

DMARC is an email authentication protocol that allows you specify deliverability policies and receive reports on messages that fail authentication: https://dmarc.org/

Of course, GetResponse can send messages in compliance with any DMARC policy, ensuring that SPF and DKIM authentication are aligned appropriately with your domain. This “Custom DKIM Authentication” feature is available on “Max” and above pricing plans.