Email Deliverability Testing and Sender Reputation Checks

Why Deliverability Testing Matters — And What It Can Honestly Tell You

Sending emails that land in spam is worse than not sending at all: you burn through your list, damage your sending reputation, and never learn why. Deliverability checks exist to surface the problems you can still fix — authentication that was never published, a domain that quietly got listed, copy that reads like a promotion — before those problems cost you a campaign.

It is worth saying plainly what no email platform can do, including this one. Once your message reaches a prospect's provider, nobody outside that mailbox can see which folder it landed in. Any tool claiming to show real inbox placement for your live campaign is either guessing or reporting on its own test mailboxes rather than yours. WarmySender takes the other approach: we show the signals we can genuinely observe, we tell you when a number is not trustworthy yet, and we do not fill the gaps with estimates.

What We Actually Measure About Placement

Warmup is where real placement data comes from. Every warmup email travels between mailboxes inside the network, so both ends are visible to us — which means the receiving mailbox can be opened over IMAP, the message located, and its landing recorded exactly: inbox or spam.

From that, each mailbox gets:

• Inbox rate — the share of located warmup emails that reached the inbox, calculated as inbox divided by inbox plus spam. Messages we could not locate and messages that bounced are deliberately excluded, so a connection hiccup never masquerades as a spam hit.
• Spam rate — the mirror image of the same figure.
• Bounce rate, reply rate and detection rate — how much warmup mail failed outright, how much drew a reply, and what share of sends we managed to locate at all.
• Warmup score (0-100) — one figure that starts at 100 and subtracts penalties: half a point per point of spam rate, two points per point of bounce rate, and three-tenths of a point for every point the inbox rate sits below perfect. A mailbox with no data returns no score at all, rather than a flattering 100.

The 20-email rule. Until a mailbox has at least 20 warmup emails we could actually locate, the interface shows "Building data" instead of a percentage. A 50% inbox rate calculated from two emails is noise, and showing it would only invite you to act on nothing.

A daily trend, not a snapshot. Counts are stored per mailbox per day, giving you a 7-day view and a 30-day timeline. Direction matters far more than any single day: a mailbox drifting steadily downward over a fortnight is a story, one bad Tuesday is not.

Read this number for what it is. It measures our own warmup mail moving between peer mailboxes. That makes it a reputation signal for the sending account — genuinely useful, and the closest honest proxy available — but it is not a measurement of where your campaign emails land. On the campaign side, "delivered" means the receiving server accepted the message. It does not mean the message reached the inbox.

Spam Rescue During Warmup

When a warmup email is found in the spam folder, WarmySender does more than log it. The receiving mailbox moves the message to the inbox over IMAP, waits a randomized five to thirty seconds so the sequence does not look mechanical, marks it as read, and stars it roughly a quarter of the time — the pattern a real person leaves behind when they dig a message out of spam.

The honest caveat: rescuing a message does not erase the spam landing from your numbers. That first placement is recorded permanently against the sending mailbox, because it is the signal you need to see. Rescue is a positive engagement action on the receiving side; it is not a provider feedback loop, and it is not a way to make a bad inbox rate look good.

Authentication Checks: SPF, DMARC, and the Truth About DKIM

When you connect or test a mailbox, WarmySender looks up your sending domain's DNS and reports on its mail records: whether MX is present, whether an SPF record exists, and whether DMARC is published — including which policy it declares, since a policy of none behaves very differently from quarantine or reject.

DKIM is deliberately not checked, and we say so rather than showing a green tick. A DKIM public key lives at a name built from a selector your provider chose, and there is no DNS query that lists the selectors on a domain. Without the exact selector, DKIM cannot be verified from outside your provider. Guessing would produce a confident wrong answer, which is worse than no answer.

That reflects a rule applied everywhere on this page: a check that could not complete is not a failed check. Every result records whether it ran separately from whether it passed, so an unreachable DNS server is never reported to you as a broken SPF record.

Domain Blocklist Monitoring

A listed sending domain will quietly wreck deliverability long before your open rate makes it obvious, so WarmySender watches for it continuously instead of waiting to be asked.

What is checked: two domain-reputation blocklists — Spamhaus DBL and SURBL. Both are domain-based, which is what matters for a domain sender. We do not run IP-level blocklist checks, and we do not claim to monitor fifty lists.

How often: the monitor runs automatically every two hours. A domain that comes back clean is rechecked every twelve hours; a domain that is listed is rechecked every two hours, so a successful delisting clears quickly instead of leaving a stale warning on your dashboard. There is no "check my domain now" button, because the check is already running without you.

What is covered: your sending domains, plus verified custom tracking domains. A listed tracking domain poisons every link in every email that carries it, and it is the failure people miss most often.

Spam-Risk Score in the Campaign Builder

As you write a campaign email, WarmySender scores it live in your browser on a 0-100 scale where higher is worse. Green is 30 or below, yellow runs 31 to 60, red is anything above 60. The same score appears again in the pre-launch checklist, so a draft that drifted while you edited it does not slip out unnoticed.

The eight checks, in full:

• Spam-trigger phrasing, drawn from a 141-term list, with a ceiling so one unlucky word cannot dominate the score
• ALL-CAPS words, measured against a whitelist of ordinary abbreviations so ROI and CEO are not punished
• Exclamation marks beyond the first
• Link density — how many links you use relative to how much you actually wrote
• Personalization: using merge tags lowers your score, using none raises it
• Body length, penalized at both extremes — a near-empty email and a five-thousand-character wall both read badly
• URL shorteners, which filters treat as an attempt to hide a destination
• Image-to-text ratio, with image-only emails penalized hardest

What it is not. This is a static checklist reading your copy in your browser. It sends nothing, contacts no provider, simulates no spam filter, and does not look at your authentication. The result is not stored and not trended — it is a writing aid, and we publish no accuracy figure for it because we have run no study that would justify one. Treat a red score as a prompt to reread your draft, not as a prediction of where the email will land.

Bounce Protection That Actually Runs

The fastest way to wreck a sending reputation is a bad list, so the guard against it is automatic. If a campaign's bounce rate climbs past its ceiling — 5% by default, and yours to change — the campaign pauses itself. The check only applies once the campaign has sent at least 50 emails, because a bounce on send number three is a coin flip, not a trend.

When you clean the list and resume, the ceiling is measured against a fresh window rather than the damage already recorded, so a genuinely fixed campaign is not paused again a minute later. Addresses that bounce are suppressed from future sends, and a suppression is only applied more broadly once the same address has failed for more than one account — one misconfigured sender cannot poison the pool for everybody.

The cheapest bounce protection, though, happens earlier: real-time email verification on your list before you import it, so bad addresses never reach a send at all.

The WarmySender Advantage: Complete Testing Starting at $14.99/month

Every check on this page is included in every plan, starting at $14.99/month — warmup placement tracking and the warmup score, spam rescue, SPF and DMARC checks, continuous domain blocklist monitoring, the live spam-risk score, and automatic bounce protection. No deliverability add-on, no per-test charge, and no invented numbers to make the dashboard look better than reality.