DMARC requires SPF alignment — the domain in the MAIL FROM/Return-Path must match your From: domain. If you’re using a third-party sender (e.g., Mailchimp, SendGrid) that uses their own Return-Path domain, SPF will pass on their domain but won’t align with your From: domain. The fix: configure DKIM signing from your domain with that service, which provides DKIM alignment instead.
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