Email Deliverability for DTC Brands: SPF, DKIM, and Sender Reputation Explained

We get asked to fix “bad email performance” more often than we get asked to fix deliverability directly, but they’re frequently the same problem. A flow with sharp copy and smart segmentation can’t outperform a domain that’s landing in spam. Deliverability is the floor everything else sits on.

SPF, DKIM, and DMARC, in Plain Terms

These three records live in your domain’s DNS settings and together tell mailbox providers your email is legitimate.

• SPF (Sender Policy Framework): A list of servers authorized to send email on your domain’s behalf. Without it, a receiving server has no way to confirm your ESP is allowed to send as you.
• DKIM (DomainKeys Identified Mail): A cryptographic signature attached to each email, proving it wasn’t altered between sending and delivery. It’s how a receiving server confirms the message is authentic, not spoofed.
• DMARC (Domain-based Message Authentication, Reporting and Conformance): The policy layer on top of SPF and DKIM. It tells receiving servers what to do when a message fails authentication (quarantine, reject, or do nothing) and asks for reporting on failures so you can catch problems.

Klaviyo, like most modern ESPs, walks you through setting these up during domain authentication. Skipping this step, or leaving records misconfigured, is one of the most common root causes we find when auditing an account with a spam-folder problem.

Authentication Gets You In the Door. Reputation Keeps You There.

Passing SPF and DKIM doesn’t guarantee inbox placement. Mailbox providers like Gmail, Outlook, and Yahoo track sender reputation continuously: how often recipients open, click, reply, mark as spam, or delete without reading. A domain with a history of low engagement gets throttled toward spam even with perfect authentication, because reputation is a moving signal, not a one-time check.

List Hygiene Is a Deliverability Practice, Not Just a List-Size Decision

This is where list hygiene and deliverability directly connect. Mailbox providers evaluate engagement at the domain level, not just per-subscriber. A list padded with unengaged addresses drags down the aggregate engagement rate mailbox providers see for your entire sending domain, which lowers inbox placement even for the subscribers who do want your emails.

Suppressing unengaged subscribers, ideally after a genuine win-back attempt, isn’t just a list-cleanliness habit. It’s one of the most direct levers you have on inbox placement for your active subscribers.

→ Full case study: 70.7% open rate, e-commerce open rate system

Sending Patterns Matter Too

A sudden spike in send volume, especially from a domain with limited sending history, can trigger spam filtering on its own, independent of content or list quality. New domains and newly warmed IPs benefit from a gradual ramp in volume rather than an immediate jump to full list size. Consistency in sending cadence also helps: mailbox providers build a reputation baseline around your normal patterns, and abrupt deviations from that baseline can trigger closer scrutiny.

The Order of Operations

If open rates are underperforming, the fix order matters. Authentication (SPF/DKIM/DMARC) first, because nothing else works if the domain isn’t trusted. List hygiene second, because engagement signals are what sustain reputation over time. Copy and flow strategy last, because copy improvements can only show their real impact once the infrastructure underneath them is sound.