How a deep deliverability audit reversed 15 months of click erosion, surfaced hidden Gmail routing issues across two Klaviyo programmes, and built a foundation for sustainable engagement growth.
Our client is a well-established food media publisher with a loyal, subscription-driven audience spanning recipe content, editorial letters, cooking radio, and a curated kitchen products store. Email sits at the heart of both their editorial relationship with readers and their commercial revenue from product promotion.
With two separate Klaviyo programmes serving distinct subscriber needs, the publisher commissioned Postbox Services for an independent, data-grounded audit across their full send history - to understand why engagement had been declining for over a year, and what it would take to reverse it.
Weekly recipe content, editorial letters, and radio promotion sends - served across segmented lists throughout the audit period, with an engaged subscriber segment deployed for recipe sends. High brand affinity, but click engagement showing a measurable and sustained decline that open rate metrics were obscuring.
Product promotions, discount announcements, and preview sends targeting active shoppers. Click performance had declined approximately 40% over 15 months - compounding commercial risk. Seed testing subsequently revealed near-total Gmail Promotions tab routing, invisible in Klaviyo dashboards throughout the period.
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Platform-level metrics told an incomplete story. Open rates appeared broadly stable. List sizes were healthy. But beneath the surface, the signals pointed to a programme in slow decline - and a routing reality that no standard dashboard was surfacing.
"Click rates had been falling across both programmes for over a year. Without knowing where emails were actually landing in Gmail - Primary Inbox, Promotions tab, or Spam - there was no way to know whether the problem was content, timing, audience quality, or deliverability itself. The audit separated the signal from the noise."
Across the full 15-month dataset, editorial click rates declined materially across all content types. The sharpest drops were in recipe and radio sends. Open rate data - inflated by MPP - masked the severity; click data exposed it.
Store programme sends experienced a persistent downward trend in clicks - approximately 40% over the audit window. With promotional sends relying on click-through for commercial conversion, this trajectory represented compounding revenue risk if left unaddressed.
Seed testing revealed that Store sends were routing to the Promotions tab for the vast majority of Gmail subscribers with 6+ months of account history - at approximately 95% tabs / 5% inbox. This routing reality was entirely invisible in Klaviyo's native reporting and had been operating as a silent headwind on engagement throughout the period.
The editorial programme operated across multiple list configurations during the audit period - including segmented lists running in parallel with an engaged-only cohort for recipe sends. Without precise structural documentation, consistent trend analysis was not possible from campaign data alone.
No seed testing or structured placement tracking existed before the audit. The publisher's use of Klaviyo's shared IP infrastructure also meant that certain third-party monitoring tools (such as SNDS) were not available, leaving the programme with limited real-world routing visibility.
Postbox Services delivered a comprehensive deliverability audit across both programmes - precisely mapping the causes of engagement decline, validating assumptions against seed test data, and producing a prioritised, owner-mapped recommendation set with clear implementation logic.
Within two quarters of implementing the audit recommendations, both programmes began showing consistent improvement across engagement, routing quality, and list health - positive trajectories across Editorial and Store for the first time in over a year.
"Before the audit, we assumed our email programme was in reasonable health - open rates looked fine. What Postbox uncovered was that click engagement had been declining for over a year across both programmes, and almost all our Store sends were landing in Gmail's Promotions tab. We didn't know what we didn't know. The audit gave us clarity - and the recommendations gave us a clear path forward."
"The depth of analysis was exceptional. They didn't just report what the numbers said - they explained why, validated each finding against seed test data, and made sure every conclusion was directly supported by the underlying evidence. That rigour matters when you're making infrastructure and content decisions for a brand people trust."
"The Gmail routing discovery alone was worth the entire engagement. We had no idea Store sends were hitting Promotions at that rate. There was simply no way to know without the seed testing Postbox ran. That single insight completely reshaped how we thought about our Store programme strategy and where to invest for commercial impact."
Post-MPP, open rate data is largely unreliable as a proxy for inbox placement or genuine engagement. Click rates - combined with systematic seed testing - are the only dependable signals for real-world routing health.
Editorial and Store sends behave differently at ISPs. Store sends attract commercial classification signals that editorial sends don't carry. Routing figures from one programme cannot be applied to the other without verification.
When list structures evolve mid-period - parallel lists, new segments, retired cohorts - documentation must keep pace. Structural clarity is essential for accurate benchmarking and trend attribution.
Sunset flows triggered by open inactivity alone miss genuinely disengaged subscribers in a post-MPP world. Click-based thresholds surface true disengagement more accurately and protect sender reputation more effectively.
Fifteen months of unmonitored decline compounded into significant programme risk. A lightweight quarterly health check would have surfaced the click trend far earlier - at a fraction of the remediation cost.
This engagement represents a real client audit. Client details have been anonymised to protect confidentiality. Outcomes and methodologies accurately reflect the work delivered.
If your click rates are declining and you don't know why - or if you've never run a seed test to see where your emails actually land - let's talk. A deliverability audit is the fastest way to go from guessing to knowing.
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