The DMARC compliance percentage is the ratio of the messages with DMARC evaluation passed to the total of messages sent from the domain.
DMARC is considered passed when either SPF evaluation or DKIM evaluation passes.
There are two ways to achieve DMARC validation: using SPF and using DKIM.
To comply with DMARC through SPF, you need to use a custom SPF domain (Return-Path domain or Mail FROM domain), because SPF validation requires the domain in the From address to match the SPF domain. By using your own SPF domain, you have the flexibility to use SPF, DKIM, or both to achieve DMARC validation.