How we score deliverability
No black box. Flash's score is a deterministic function of signals mailbox providers actually act on — the same email always scores within ±3 points. No LLM is anywhere in the scoring path. Here's exactly what we measure, how it's weighted, and what we refuse to do.
The weights
A complete score is out of 100, across five components:
- Inbox placement — 55. Does the message land in the inbox vs spam at real Gmail, Outlook and Yahoo seed inboxes. The thing every other check only predicts.
- Authentication — 15. SPF, DKIM, and DMARC, read as an enforcement verdict — not "is SPF present" but "will a mailbox provider accept this identity." DMARC
p=noneis flagged as unprotected even though it technically passes. - Content — 10. Spam-pattern matching on the decoded message body (MIME/HTML decoded first), text-to-image balance, link density.
- Blacklist — 10. The connecting IP against Spamhaus ZEN and Barracuda. Shared provider relays (Gmail/Outlook/SES) are skipped — their reputation isn't yours to own.
- Hygiene — 10. Date and Message-ID headers, and the one-click List-Unsubscribe header now required of bulk senders.
Setup grade vs. full score
Until inbox-placement seeds are measured for your test, that 55-point component isn't counted as zero — it's excluded, and we show a letter grade for your setup (auth + content + blacklist + hygiene) instead. A perfect configuration reads as an "A," never "42 / failing." Once placement is measured, the score becomes a true composite out of 100.
What we deliberately refuse to do
No LLM in the scoring path. Every point is a rule with a one-sentence reason. A language model can't be audited or reproduced; a rule can.
No publishing a score for a domain you don't control. A public share card requires the From-domain to be DMARC-aligned or DNS-verified — so no one can spoof a competitor and publish a damaging "0/100."
No DNSBL-ing shared relays. If you send through Gmail/Outlook/SES, that IP's reputation is the provider's, not yours — we don't penalize you for it.
No vanity inflation. We'd rather show an honest "placement not measured yet" than a confident number we didn't earn.