Email Deliverability Basics: Land in the Inbox, Not Spam
SPF, DKIM, DMARC, and warm-up explained without the jargon.
Email deliverability is whether your email actually reaches the inbox — versus landing in spam, or not arriving at all. It's determined mostly by three DNS records, how quickly you started sending at volume, and what's actually inside the email. None of it is mysterious once you see the pieces.
If your open rates have quietly dropped, or a new sending domain isn't landing anywhere useful, the fix is almost always one of the items below.
It helps to be clear about what deliverability actually measures. "Delivered" in most dashboards just means the receiving mail server accepted the message — it says nothing about whether that message landed in the inbox, the promotions tab, or spam. Inbox placement is the metric that actually matters to a reader ever seeing your email, and it's shaped by the factors below, not by whether the send technically succeeded.
The three DNS records that matter
Every mailbox provider (Gmail, Outlook, Yahoo) checks these three records before deciding whether your email is trustworthy:
SPF (Sender Policy Framework) — a DNS record listing which mail servers are allowed to send email on behalf of your domain. Without it, anyone could spoof yourcompany.com and mailbox providers have no way to tell the difference.
DKIM (DomainKeys Identified Mail) — a cryptographic signature attached to every email, proving it wasn't altered in transit and genuinely came from a server you authorized. Think of it as a tamper-proof seal.
DMARC (Domain-based Message Authentication) — a policy record that tells receiving servers what to do if SPF or DKIM checks fail (quarantine, reject, or do nothing), and where to send reports about failures.
WaSMS generates the exact SPF and DKIM records for your sending domain and shows you exactly what to paste into your DNS provider — no manual key generation needed.
TXT record example (SPF):
v=spf1 include:spf.brevo.com ~all
DKIM record example:
brevo._domainkey.yourdomain.com → provided by WaSMS setup screen
Skipping SPF and DKIM doesn't just risk spam folder placement — some providers reject unauthenticated mail outright. This is the one setup step that's not optional.
Why DMARC is worth the extra ten minutes
SPF and DKIM alone get most senders most of the way, but DMARC closes an important gap: without it, a receiving server that sees a failed SPF or DKIM check has to guess what to do — some quarantine the message, some deliver it anyway, some reject it, all inconsistently. A DMARC record removes the guessing by explicitly stating your policy, and it gives you visibility through aggregate reports showing who's sending email that claims to be from your domain, which is often the first sign of a spoofing attempt against your brand.
Warming up a new domain
A brand-new sending domain has no reputation with mailbox providers yet. Sending 5,000 emails on day one from a domain that's never sent anything looks exactly like spam behavior, even if every recipient asked for it.
A safe warm-up looks like this:
- Week 1: Send to your most engaged contacts only — people who've opened your emails before, or recent customers. Keep volume low (a few dozen to a few hundred a day).
- Week 2–3: Gradually increase volume, watching open rates and bounce rates as you go.
- Week 4+: Once open rates are stable and bounces are low, scale toward your normal sending volume.
An agency called Bright Signal ramped a new client domain this way over three weeks before sending their first full newsletter blast — inbox placement stayed above 95% because the domain had already built a track record with major providers by the time volume ramped up.
The instinct to skip warm-up is understandable — nobody wants to wait three weeks before sending a launch campaign to their full list. But the alternative isn't faster, it's just failure deferred: a domain that blasts full volume on day one typically sees inbox placement collapse within days, and recovering from that damaged reputation takes far longer than the warm-up period would have.
Content triggers that flag spam
Beyond authentication, what's actually in the email matters:
- Spammy phrases — "act now," "100% free," excessive exclamation marks or all-caps subject lines
- Link-heavy emails with little text — a wall of links and one line of text reads as spam to filters
- Image-only emails — no text content at all is a classic spam pattern
- Missing unsubscribe link — required by law in most regions, and its absence is itself a red flag to filters
- Mismatched sender name and reply-to domain — sending "from" one brand but replying "to" an unrelated address
None of this means your emails need to be plain-text and boring — it means balance text and images, keep language natural, and always include a working unsubscribe link.
Monitoring bounces and complaints
Two numbers tell you almost everything about domain health:
- Bounce rate — should stay under 2%. A spike usually means your list has stale or invalid addresses; clean the list rather than keep re-sending to dead addresses.
- Complaint rate (recipients marking as spam) — should stay under 0.1%. A rising complaint rate is the fastest way to damage domain reputation, even if every message technically has consent.
WaSMS surfaces both metrics per campaign, so a spike is visible before it becomes a pattern. If either number climbs, pause sending and investigate the list segment responsible rather than continuing at the same volume.
Reading the numbers correctly
A single bounce doesn't mean much — addresses go stale constantly as people change jobs or abandon accounts. What matters is the trend and the type. A "hard bounce" (the address doesn't exist) should trigger automatic suppression so you never send to it again; a "soft bounce" (mailbox full, server temporarily down) can be retried. If your hard bounce rate is climbing steadily rather than staying flat, that's usually a sign your list is aging and needs a cleaning pass, not that anything about your sending changed.
When to switch senders
If bounces and complaints stay low but inbox placement is still poor, the issue may not be your domain — it may be the specific sending infrastructure. Test by sending the same content through a different verified sender address and comparing inbox placement using a seed-list test (a small group of test accounts across Gmail, Outlook, and Yahoo).
If you're also evaluating whether your current provider's free tier is the constraint, see SendGrid Alternative: A Free Path That Actually Works for a direct comparison of what changes and doesn't when switching.
It's also worth ruling out the simplest explanation before assuming infrastructure is at fault: a spike in unsubscribes or a specific subject line pattern getting flagged can look identical to an infrastructure problem in the numbers, but the fix is entirely different — adjust the content or list, not the sending platform. Run a seed-list test before switching anything, so you know which layer of the problem you're actually solving.