Email Deliverability
Email deliverability is whether your emails reach the inbox or land in spam. It is shaped by sender reputation, technical authentication and list hygiene.
Email deliverability is whether your emails reach the inbox, not just whether they were technically sent.
What Email Deliverability Means in Marketing
You can send a perfect email. The right subject line, the right offer, the right time. None of it matters if the email lands in spam.
Deliverability is the set of factors that determine inbox placement. It sits below the surface of most email marketing dashboards, visible only when something goes wrong: open rates fall unexpectedly, a campaign generates zero responses, or you discover your domain has been flagged by a major inbox provider.
The core issue is trust. Gmail, Outlook and other inbox providers have strong commercial incentives to keep spam out of their users’ inboxes. They use a combination of technical signals and engagement signals to decide how much to trust each sender. Senders with strong trust get inbox placement. Senders with weak trust get spam, and senders who violate enough rules get blocked entirely.
How Email Deliverability Works
Deliverability is determined by two categories of signals:
Technical authentication:
- SPF (Sender Policy Framework): a DNS record that lists the IP addresses allowed to send email from your domain.
- DKIM (DomainKeys Identified Mail): a cryptographic signature added to each email that proves it was sent by your server and not modified in transit.
- DMARC (Domain-based Message Authentication, Reporting and Conformance): a policy record that tells receiving servers what to do if SPF or DKIM checks fail.
Without these three configured correctly, inbox providers treat your email as suspicious before it arrives.
Engagement reputation:
- Open rate: if subscribers regularly ignore your emails, providers learn to route them away from the inbox.
- Spam complaints: even a small percentage of recipients marking your email as spam damages your sender score rapidly.
- Bounce rate: high hard bounce rates signal that you are sending to addresses that do not exist.
- List age and hygiene: old unengaged lists generate the signals above without ever converting.
Email Deliverability Example
A SaaS company reactivates their entire email list after six months of inactivity. Half the list has not opened an email in over a year. The reactivation campaign generates a 4% spam complaint rate, which is catastrophic. Gmail deprioritises all future sends from the domain. Open rates drop from 28% to 9% across all campaigns, including to active subscribers. Recovering takes months of careful sending to small, highly engaged segments.
Why Email Deliverability Matters for Marketers
Email revenue depends on emails being seen. A list with poor deliverability is not a marketing asset. It is a liability that actively damages your domain reputation each time you send.
The good news is that deliverability problems are almost entirely preventable. Technical authentication takes an afternoon to configure correctly. List hygiene is a matter of removing subscribers who have not engaged in six to twelve months. The investment is small relative to the value of having your emails reliably reach the people you paid to acquire.
Frequently Asked Questions
What is the difference between delivery rate and deliverability?
Delivery rate measures whether the receiving mail server accepted your email at all. Deliverability describes whether it reached the inbox rather than the spam folder. An email can be delivered in the technical sense but land in spam, where it will never be seen. Delivery rate is binary. Deliverability is about placement, and it is harder to measure directly.
What are the three main technical records needed for good deliverability?
SPF, DKIM and DMARC. SPF specifies which servers are authorised to send email on behalf of your domain. DKIM adds a cryptographic signature to each email that proves it has not been tampered with. DMARC tells receiving servers what to do if an email fails SPF or DKIM checks: quarantine it, reject it, or let it through. All three work together. Having one without the others leaves gaps.
Why does sending to an old or unclean list hurt deliverability?
Sending to invalid addresses generates hard bounces, which signals to inbox providers that you are not maintaining your list. Sending to disengaged subscribers who never open generates low engagement signals, which trains the algorithm to route your emails to spam. Spam trap addresses embedded in purchased or scraped lists can get your domain blocklisted. A smaller, clean list almost always outperforms a large dirty one.