Return-Path and From are separate email fields, and mismatched domains can trigger DMARC failures

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Every email carries two sender identities: the From header visible to recipients and the envelope sender used by receiving servers for bounces and SPF checks. When these point to different domains, DMARC can fail even though SPF and DKIM pass for the provider's domain, often sending mail to spam without a clear error. DMARC requires at least one of SPF or DKIM to align with the From domain. Recommended fixes include signing with your own domain and using a return-path subdomain you control, or using the provider's domain for both identities. Bounce messages go to the envelope sender, so a black-hole return-path means dead mailboxes go unnoticed. Testing involves checking the Authentication-Results header of a message sent to a personal Gmail account.

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