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 main inbox. Not the spam folder. Not the promotions tab. Not a catch-all folder no one reads. A few things decide it. Your tech setup counts, and so does your sender reputation. List hygiene and engagement signals count too. Most marketers set deliverability up once and move on. The ones who hit 95%+ inbox rates treat it as an ongoing habit.
Deliverability problems show up in almost every email program we take over from another agency. The signs are always the same. Open rates fall. Unsubscribes rise. Spam complaints pop up at times. The account can look fine on the surface. But 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 mail servers which IP addresses may send email for your domain. DKIM (DomainKeys Identified Mail) adds a signed stamp to each email. That lets receivers check that 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. You can then see who sends mail from your domain. In 2024, Google and Yahoo made the rules tighter on all three. The new rules cover senders of more than 5,000 emails a day. Without proper DKIM and SPF alignment, emails are more likely to be blocked 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 that score. Your spam complaint rate matters, so keep it below 0.1% for Gmail. Your hard bounce rate matters, so keep it below 2%. Your unsubscribe rate matters too. Most of all, engagement matters. Gmail is known to filter on whether people open, click, or reply. 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
Clear out hard bounces right after any campaign. A pile-up of them is one of the fastest ways to hurt sender reputation.
Suppress contacts who have not opened in 180 days before you send large campaigns. Send a re-engagement sequence first. If there is no reply, remove them.
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 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.
Every TTGC email program starts with a deliverability audit. We do it before a single send goes out. See email marketing vs paid ads to see how it fits your wider channel choice. Start with a growth assessment and we will review your email setup.
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.
