MarketingPlatform supports full DMARC compliance.
Information on configuring the service for DKIM found here: https://marketingplatform.com/da/sadan-anvendes-spf-og-dkim/
The SPF addition MarketingPlatform recommends is 'include:mailmailmail.net', however that currently has only 1 IP range in it - so another way of authorizing their servers without using up 1 DNS lookup would be 'ip4:91.235.232.0/24'. This however can break your SPF authentication if MarketingPlatform changes that range so use at your discretion. More on SPF setup can be read here: https://marketingplatform.com/da/sadan-anvendes-spf-og-dkim/