The DMARC compliance percentage is the ratio of the number of messages the DMARC evaluation passed over the total number of messages sent from your domain.
There are two ways to achieve DMARC validation: using SPF and using DKIM.
Your DMARC is considered passed when either your SPF evaluation or your DKIM evaluation passes.
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.