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.
Email deliverability is the ability of your email to reach the recipient's primary inbox - not their spam folder, not their promotions tab, and not a catch-all folder nobody reads. It is determined by a combination of technical setup, sender reputation, list hygiene, and engagement signals. Most marketers treat deliverability as a one-time setup task. The ones who consistently hit 95%+ inbox placement rates treat it as an ongoing discipline.
Mherie encounters deliverability problems in nearly every email program TTGC inherits from other agencies. The symptoms are always the same: declining open rates, increasing unsubscribes, occasional spam complaints - and an account that looks fine on the surface while 30-40% of emails never reach the intended inbox.
The Technical Foundation: SPF, DKIM, and DMARC
These three DNS records are the minimum viable technical setup for any sending domain. SPF (Sender Policy Framework) tells receiving mail servers which IP addresses are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each email so receivers can verify it was not tampered with in transit. DMARC (Domain-based Message Authentication, Reporting & Conformance) tells receivers what to do if SPF or DKIM fails - and sends you reports so you can see who is sending from your domain. Google and Yahoo tightened enforcement of all three in 2024 for senders sending more than 5,000 emails/day. Without proper DKIM and SPF alignment, emails are increasingly likely to be rejected or filtered.
Sender Reputation: The Score You Do Not See
Every sending domain and IP address accumulates a reputation score with inbox providers (Gmail, Outlook, Yahoo). This score is influenced by: spam complaint rate (keep below 0.1% for Gmail), hard bounce rate (keep below 2%), unsubscribe rate, and - most importantly - engagement. Gmail in particular is known to filter based on whether recipients open, click, or reply to your emails. A list of 50,000 unengaged subscribers will destroy deliverability faster than a list of 5,000 highly engaged ones.
List Hygiene: The Deliverability Practice Nobody Wants to Do
Remove hard bounces immediately after any campaign. Hard bounce accumulation is one of the fastest ways to damage 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 reduces list size but dramatically improves engagement rates and reduces spam traps.
Never purchase email lists. Purchased lists contain spam traps - addresses maintained by inbox providers specifically to identify and penalize senders. One spam trap hit can blacklist your domain.
The single most impactful deliverability decision is to send less, not more. Reducing send frequency while increasing relevance raises engagement rates, which signals to inbox providers that 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.
