Whether a message's From address belongs to the domain this account onboarded for sending.
A mismatch restricts delivery rather than failing: Cloudflare accepts a send from a domain with
no SPF or DKIM and delivers it only to verified destination addresses, so registration mail is
accepted by the API and never arrives. A subdomain of the sending domain passes.
Parameters
from: string
the effective sender, which is senderFor()'s answer rather than MAIL_FROM
sending: string
the onboarded sending domain, or '' when none; empty answers ok (a third-party
relay has no Cloudflare sending domain)
Whether a message's From address belongs to the domain this account onboarded for sending.
A mismatch restricts delivery rather than failing: Cloudflare accepts a send from a domain with no SPF or DKIM and delivers it only to verified destination addresses, so registration mail is accepted by the API and never arrives. A subdomain of the sending domain passes.