Bob owns the domain
bob.combut doesn't manage an emailing server. Instead he uses an email forwarding service (provided by his registrar / DNS service, for example Cloudflare does this), redirecting every email arriving on
[email protected]. Let's say this forwarding server has IP
This means that the email forwarding service actually modifies the original email from Alice and resends an email:
From: [email protected]
To: [email protected]
When arriving by Yahoo,
yahoo.com will check if this email is legitimate. Since the email's
[email protected], it will check the SPF of domain
example.com. But the "email forwarding server IP"
126.96.36.199 is not listed in
example.com's SPF DNS records! This means
yahoo.com should probably refuse this email.
Based on this, how can an email forwarding service even work at all? It shouldn't, based on the fact its servers' IP arent't listed in the original sender's domain's SPF. Still these email forwarding services work very well and reliably. How is this possible?
I'm probably missing a piece of the puzzle, which one is it?