Glossary · Mailboxes
Email forwarding automatically resends incoming mail to another address. It's convenient, but it can break SPF and DMARC along the way.
When a server forwards a message, it delivers it from its own IP, which isn't in the original sender's SPF record, so SPF fails. DKIM usually survives if the message isn't modified, which is often what keeps forwarded mail passing DMARC.
Good forwarders rewrite the envelope sender (the Sender Rewriting Scheme) and add ARC headers. Forwarding everything to a personal inbox is a common stopgap, but replies then come from the wrong address; hosting the domain's mailboxes properly avoids both problems.
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