What Is Email Deliverability and Why Your Campaigns Keep Landing in Spam
The invisible infrastructure layer that determines whether your emails reach inboxes or disappear — and what actually controls it.
So what is email deliverability? It is your email's ability to reach the recipient's main inbox. Not the spam folder. Not the promotions tab. Not a catch-all folder no one reads. A few things decide it. These include your technical setup, your sender reputation, your list hygiene, and your engagement signals. Most marketers treat deliverability as a one-time setup. But the ones who hit 95%+ inbox rates treat it as an ongoing habit.
Deliverability problems show up in nearly every email program inherited from another agency. The symptoms are always the same. Open rates fall. Unsubscribes rise. Spam complaints pop up now and then. The account can look fine on the surface. Meanwhile, 30 to 40% of emails never reach the inbox.
The Technical Foundation: SPF, DKIM, and DMARC
These three DNS records are the bare minimum for any sending domain. SPF (Sender Policy Framework) tells receiving mail servers which IP addresses may send email for your domain. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each email. That lets receivers confirm no one changed it on the way. DMARC (Domain-based Message Authentication, Reporting & Conformance) tells receivers what to do when SPF or DKIM fails. It also sends you reports, so you can see who is sending from your domain. In 2024, Google and Yahoo tightened the rules on all three. This applies to senders who send more than 5,000 emails a day. Without proper DKIM and SPF alignment, emails are more likely to be rejected or filtered.
Sender Reputation: The Score You Do Not See
Every sending domain and IP address builds a reputation score with inbox providers like Gmail, Outlook, and Yahoo. A few things shape this score. Your spam complaint rate matters (keep it below 0.1% for Gmail). Your hard bounce rate matters (keep it below 2%). Your unsubscribe rate matters too. Most of all, engagement matters. Gmail is known to filter based on whether people open, click, or reply to your emails. A list of 50,000 cold subscribers will wreck deliverability faster than a list of 5,000 engaged ones.
List Hygiene: The Deliverability Practice Nobody Wants to Do
Remove hard bounces right after any campaign. A pile-up of hard bounces is one of the fastest ways to hurt sender reputation.
Suppress unengaged contacts (no open in 180 days) before large campaigns. Send a re-engagement sequence first - if no response, remove.
Use double opt-in for all new subscribers. It shrinks your list size but sharply lifts engagement and cuts spam traps.
Never buy email lists. Bought lists hold spam traps. These are addresses that inbox providers keep just to catch and punish senders. One spam trap hit can blacklist your domain.
The single most powerful deliverability move is to send less, not more. Send less often, but make each email more relevant. That lifts engagement. Higher engagement tells inbox providers your email is wanted. And wanted email gets delivered.
TTGC email programs include a deliverability audit as the first step in every engagement - before a single send goes out. See email marketing vs paid ads for how deliverability fits into the broader channel decision. Start with a growth assessment to get your email infrastructure reviewed.
Audit Your Email Deliverability
Book a free Brand and Growth Assessment and see exactly how Through The Glass Creatives would approach it.
Sources
- Google, "Gmail Sender Guidelines Update 2024," Google Support, 2024.
- Mailgun, "The Email Deliverability Guide 2025," Mailgun.com, 2025.
- Return Path / Validity, "Sender Score and Email Deliverability," Validity.com, 2025.
- Litmus, "State of Email Deliverability 2025," Litmus.com, 2025.
