Every free "spam checker" scores your copy and calls it deliverability. It mostly isn't. Inbox placement is decided by authentication and reputation — so this checks your actual DNS records live, and reviews the copy separately for what copy genuinely affects: whether a human replies.
Roughly in order of weight. Note where content sits.
SPF says which servers may send as you. DKIM cryptographically signs the message. DMARC tells receivers what to do when those fail, and sends you reports. Google and Yahoo now require these for bulk senders, which moved them from best practice to a hard gate. This is the half the checker above tests, live.
Complaint rate, bounce rate, how long the domain has sent mail, and how fast volume ramped. A brand-new domain sending 500 cold emails on day one is the clearest possible signal, and no wording fixes it. Nothing external can measure this — it needs your sending history.
Scraped lists produce hard bounces and spam-trap hits, both of which damage the domain reputation above. One bad send can cost months. This is the most common cause of a sudden deliverability collapse in cold outreach.
Rule-based word scoring still exists in some gateways, so it is not nothing — but it is the last of the four and the only one most tools measure. What content genuinely controls is the reply rate, and the far more damaging content effect is a recipient hitting "report spam" because your email annoyed them. That harms reputation directly.
If the SPF, DKIM or DMARC lookup shows a gap, fix it with whoever manages your domain before sending more, since copy cannot overcome failed authentication. Then compare your landing page with the Landing Page Friction Score, and see how the numbers behind your outreach look in the LTV:CAC Calculator. Our services and pricing page lists what we build.