How your messages find their way home.
Forwarded emails are increasingly landing in spam because DMARC enforcement breaks SPF authentication at the forwarding hop. ARC signing preserves the authentication chain, so Gmail and Yahoo still trust forwarded mail even when SPF fails.
SPF, DKIM, and DMARC all pass and your email still ends up in the spam folder. I ran into this exact problem with an announcement for our email forwarding service, so I dug into the headers and the broader reasons authentication alone is not enough.
How email was born in 1971 — nearly two decades before the web — and grew into the world's most enduring communication system.