Email deliverability preflight checker

Alignment is judged from header and link domains only: nothing here queries DNS, so SPF, DKIM validity, and DMARC policy are not checked. Run those record checks with your DNS provider or a lookup tool before a big send. MIME bodies are not decoded either, so a Base64 or quoted-printable raw source is scanned as pasted; the split headers-and-content mode sidesteps that. The requirement checks mirror the Google and Yahoo bulk sender rules (one-click List-Unsubscribe headers, aligned sending domains); the rest is advice, and a pass here is not a deliverability guarantee.