What’s the difference between envelope-from and header-from?

Email has two From addresses. The envelope-from (return-path) exists at the SMTP protocol level and handles bounce routing and SPF authentication. The header-from is what recipients see in their email client as the sender.

They can differ legitimately. When an ESP sends on your behalf, the envelope-from might be bounces.esp.com while the header-from shows newsletter@yourbrand.com. This works, but creates authentication challenges.

DMARC requires alignment between these addresses for at least one authentication method (SPF or DKIM). Misalignment can cause authentication failures even when both SPF and DKIM individually pass. This is why custom sending domains matter.

The envelope tells the postal service where to return undeliverable mail; the letterhead tells the recipient who wrote it. Both should point to you.