Deliverability: reaching the inbox, not the spam folder
The invisible link that decides everything
You can write the perfect email, to the perfect list, perfectly automated — if Gmail files it as spam, none of it exists. Deliverability is your emails' ability to reach the inbox. It's the most invisible and most neglected link: you don't see it as long as it works, and when it breaks, opens collapse with no apparent explanation. Understanding what decides whether an email arrives is protecting the value of the entire stack.
An email in spam isn't a poorly written email: it's an email no one will ever read, whatever its quality.
What inbox providers look at
Gmail, Outlook and the others sort every email by signals. Three families decide:
- Authentication: can you technically prove you really are the sender you claim to be?
- Sender reputation: do your domain and IP address usually send emails that people want?
- Recipient engagement: do your contacts open, click, reply — or delete and mark as spam?
You act on all three, and engagement is the most powerful: a list that interacts protects everything else.
Authentication: SPF, DKIM, DMARC
Three technical settings, done once, that prove your identity to inbox providers. SPF declares which servers are allowed to send for your domain. DKIM signs each email cryptographically, guaranteeing it wasn't tampered with. DMARC tells inboxes what to do if SPF or DKIM fails. In practice: if you send from your own domain (recommended: you@yourbrand.com, not a Gmail address), your ESP provides the records to copy at your domain host. Gmail and Yahoo now require this authentication for volume senders — it's no longer optional. Most ESPs walk you through this setup step by step.
List hygiene: clean up to deliver better
Counter-intuitive but central: a smaller, clean list delivers better than a big, soft one. Contacts who never open drag down your engagement stats, hence your reputation, hence the inbox of all your contacts. Hygiene means regularly removing bouncing addresses (no longer exist) and long-term inactives (never opened in 3-6 months, after a re-engagement attempt). Bonus: if your ESP bills by number of subscribers, cleaning up also lowers the bill. Keeping inactives "just in case" therefore costs twice: in deliverability and in money.
The traps that send you to spam
A few classic mistakes sabotage deliverability, even with good intentions:
| Trap | Why it's risky |
|---|---|
| Bought or imported list without consent | Spam complaints, trap addresses, destroyed reputation |
| Trigger words in the subject line ("FREE!!!") | Anti-spam filters, signal of bad practice |
| All-image email, no text | Classic spam signal, unreadable if image blocked |
| Sending all at once to a big cold list | Suspicious send spike, low engagement |
| No clear unsubscribe link | People click "spam" for lack of a better option |
Avoiding these traps is mostly common sense: send what people asked for, cleanly.
Warming up a domain or a list
Starting or resuming email after a pause requires gradualness. A brand-new domain suddenly sending 10,000 emails is suspicious: you ramp up volume in steps (the warm-up), starting with the most engaged contacts. Likewise, a list left cold for six months doesn't wake up with a mass send: you resume in small batches, toward those who still opened, before broadening. Some tools (and ESP options) handle this warm-up, but the principle prevails over the tool: ramp up gradually, always favoring engagement.
Key takeaways
Deliverability is the invisible link that conditions everything: an email in spam doesn't exist. Inbox providers judge authentication, reputation and especially engagement. Configure SPF, DKIM and DMARC once from your own domain — now required by Gmail and Yahoo. Practice list hygiene: remove bounces and inactives, because a clean list delivers better (and costs less). Avoid the classic traps (bought list, spam words, all-image email, no unsubscribe) and warm up domain and list gradually. Now that the email arrives, let's make it a regular appointment: the newsletter.