You can have the best subject lines in your industry, perfectly timed sends, and beautifully designed emails — and still see poor results if your deliverability is broken. Deliverability is the unglamorous side of email marketing, but it’s the foundation everything else sits on. If your emails aren’t reaching inboxes, nothing else matters.
Deliverability refers to the ability of your emails to reach your subscribers’ primary inboxes rather than landing in spam, promotions tabs, or being blocked entirely. It’s determined by a combination of technical setup, sending behaviour, and list health — and Klaviyo, used correctly, gives you the tools to manage all three.
The technical foundation starts with authentication. Three protocols — SPF, DKIM, and DMARC — tell receiving email servers that you are who you say you are, and that Klaviyo is authorised to send on your behalf. Without these properly configured on your domain, you’re sending unauthenticated email, which flags you as a potential spammer before a single subscriber has even seen your message. Klaviyo walks you through this setup, but it’s worth verifying everything is correctly in place rather than assuming.
A dedicated sending domain takes this further. By default, new Klaviyo accounts send from a shared domain. Moving to a dedicated sending domain — one that belongs exclusively to your brand — means your sending reputation is entirely your own. You’re not affected by the behaviour of other senders on a shared infrastructure, and you build domain reputation over time that compounds in your favour.
List hygiene is the ongoing practice of keeping your subscriber base clean and engaged. Every list accumulates dead weight over time — addresses that no longer exist, accounts that never open, and spam traps placed by inbox providers to catch senders with poor practices. Klaviyo’s built-in suppression management handles hard bounces automatically, but the broader work of identifying and removing chronically unengaged subscribers requires a deliberate strategy.
A sunset policy is the structured approach to this. It defines the point at which a subscriber who has shown no engagement — no opens, no clicks — over a defined period is moved to a suppression list or removed entirely. Most brands set this threshold somewhere between 90 and 180 days of inactivity. It feels counterintuitive to remove subscribers you worked to acquire, but the impact on deliverability and campaign performance is consistently positive.
Sending volume and consistency also affect deliverability. Inbox providers pay attention to sudden changes in behaviour — a brand that sends to 5,000 people one week and 50,000 the next looks suspicious. Warming up a new domain or significantly scaling your sending volume should be done gradually, increasing volume over several weeks rather than jumping straight to large sends. Klaviyo’s warm-up guidance is worth following closely if you’re in this position.
Engagement signals are increasingly central to modern deliverability. Gmail, Outlook, and Apple Mail all use engagement data — whether recipients open, click, reply, or move emails to specific folders — to determine where future messages should land. This creates a reinforcing loop: high engagement improves inbox placement, which drives more opens and clicks, which improves engagement further. The inverse is also true, which is why letting a disengaged list fester is so damaging.
Monitoring your deliverability should be a regular practice, not something you check only when results drop. Klaviyo’s deliverability dashboard gives you visibility into bounce rates, spam complaint rates, and unsubscribe rates — the key indicators of list health. Keeping spam complaint rates below 0.1% and bounce rates below 2% are widely accepted benchmarks worth tracking consistently.
The brands with the best email results aren’t just the ones with the cleverest campaigns. They’re the ones who’ve built a technical foundation that ensures their messages actually arrive. If you’re unsure whether your Klaviyo account is properly configured, get in touch — a technical audit is often the highest-leverage starting point.