Email send-safety grades

A: validated in the last 30 days, mailbox live, send. B: known engagement in the last 180 days, probably send. C: catch-all domain, your call. D: bounce, complaint, spam trap or do-not-mail, do not send. F: no signal either way. Every grade carries a reason and a date. Grades decay: an A becomes a B after 30 days without re-validation.