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Beyond the Storefront: Positioning Publisher Inventory as the Essential 'Off-Site' Extension for Retail Media Networks

Retail Media Networks are hitting inventory caps. Learn how premium publishers and SSPs can position their supply as the critical off-site growth engine for RMNs.

Beyond the Storefront: Positioning Publisher Inventory as the Essential 'Off-Site' Extension for Retail Media Networks

Beyond the Storefront: Positioning Publisher Inventory as the Essential 'Off-Site' Extension for Retail Media Networks

The narrative of the last three years in digital advertising has been dominated by one acronym: RMN. Retail Media Networks have been heralded as the "third wave" of digital advertising, following Search and Social. The logic is sound and the data is undeniable. Retailers sit on the holy grail of attribution data—actual transaction history. They know not just what users search for or who they follow, but what they actually buy. However, as we move through 2024 and look toward 2026, a structural reality is setting in. While the demand for retail data is effectively infinite, the supply of retail inventory is not. There are only so many sponsored product slots a retailer can jam onto a search results page before the user experience degrades into chaos. There are only so many banner placements on a homepage before it looks like a NASCAR jumpsuit. We are reaching the "Storefront Saturation Point." For the AdTech supply side—SSPs, premium publishers, and app developers—this represents a pivotal strategic opportunity. The next phase of RMN growth does not happen on the retailer’s domain. It happens on yours. This is the era of "Off-Site" extension, where the open web becomes the fulfillment center for retail media campaigns. At Red Volcano, we analyze the supply chain mechanics of thousands of publishers. What we are seeing is a clear bifurcation: publishers who treat RMNs as just another demand source, and publishers who are actively re-architecting their tech stack and sales narrative to become "RMN-Ready." This article explores how the supply side can capture this shifting budget.

The Inventory Ceiling and the "Off-Site" Imperative

To understand the opportunity, we must first empathize with the constraint of the retailer. Consider a major grocery chain with a robust media network. They have millions of first-party shopper profiles. CPG brands are desperate to target "lapsed yogurt buyers" or "heavy coffee drinkers." The problem is that these "heavy coffee drinkers" spend perhaps 20 minutes a week on the grocer's app or website. They spend 20 hours a week on news sites, streaming services, gaming apps, and lifestyle blogs. If the RMN relies solely on Owned & Operated (O&O) inventory, they leave 99% of the user's attention span on the table. To scale their media revenue, RMNs must decouple their data from their inventory. They must buy media elsewhere to serve ads against their data segments. This is "Off-Site" media. It is essentially audience extension, but powered by deterministic transaction data rather than probabilistic inference. For the publisher, this shifts the value proposition. You are no longer selling a "contextual impression" on a sports article; you are selling a "confirmed purchase intent" slot that happens to live on a sports article.

The Technical Convergence: How the Pipes Connect

For a publisher or SSP to capitalize on this, passive availability in the open exchange is insufficient. RMNs are risk-averse entities. They protect their shopper data with extreme jealousy. They are unlikely to simply broadcast user IDs into the bidstream for any DSP to pick up. Instead, we are seeing a shift toward curated setups involving Clean Rooms and Deal IDs.

1. The Clean Room Intermediary

The future of off-site activation is privacy-first. RMNs are increasingly utilizing Data Clean Rooms (DCRs) like Snowflake, InfoSum, or LiveRamp’s Safe Haven to match their audiences with publisher audiences without either party revealing raw PII (Personally Identifiable Information). For a premium publisher, having a distinct identity strategy is now a prerequisite for RMN partnership. If you rely solely on cookies, you are invisible to the modern RMN stack.

  • Authenticated Traffic: Publishers must prioritize strategies that encourage user logins. An email hash (HEM) is the currency of the clean room.
  • Identity Spines: Implementing solutions like UID2.0, ID5, or RampID allows the RMN to recognize their shopper on your domain.

2. Curation and PMPs

RMNs are effectively acting as agencies or curators. They prefer to buy via Deal IDs rather than the open market. This allows them to bundle specific inventory sources that match their brand safety standards and combine it with their data. From a Red Volcano perspective, when we analyze sellers.json files and supply paths, we are seeing a massive increase in "Curated Marketplaces" tailored for commerce. SSPs are building specific "Commerce PMPs" (Private Marketplaces) that bundle high-viewability, high-attention inventory specifically for RMN buyers. Here is a simplified conceptualization of how a modern Curation Record might look in a supply path analysis:

{
"curation_deal_id": "RMN-AUD-EXT-001",
"buyer": "Grocery_Chain_Media_Network",
"supply_sources": [
"premium-news-outlet.com",
"lifestyle-blog-network.com",
"cooking-app-inventory"
],
"data_overlay": "First_Party_Shopper_Data",
"kpi_target": "ROAS"
}

The publishers included in that supply_sources array are not random. They are selected based on technical fidelity, match rates, and content quality.

Structuring the Partnership: From Commodity to Partner

How does a publisher move from the "Leftover" bucket to the "Strategic Partner" bucket for an RMN? It requires a change in how you position your inventory.

The "High-Intent" Fallacy

Historically, publishers pitched their "High Intent" audiences. A tech blog claims to have "In-market laptop buyers" because the user is reading a review. That is valuable, but it is probabilistic. The RMN has deterministic data. They know the user bought a laptop yesterday. Therefore, the RMN does not need the publisher's intent data; they need the publisher's reach and context. Publishers should pivot their pitch to focus on:

  • Brand Safety & Suitability: Retailers represent CPGs who are terrified of adjacency to controversy. Premium editorial governance is a major selling point.
  • Attention Metrics: Since the RMN brings the "Who," the publisher must provide the best "Where." High viewability, low clutter, and high attention metrics (like Adelaide or MOAT scores) are critical.
  • Creative Canvas: RMNs are moving beyond standard IAB rectangles. They want Shoppable Formats. Publishers who support high-impact, video, or shoppable ad units (where a user can "Add to Cart" inside the banner) will win the off-site budgets.

The CTV Frontier: The Ultimate Storefront Extension

Connected TV (CTV) is arguably the most aggressive battleground for off-site retail media. The logic is compelling: capture the user in the living room with a brand awareness message (powered by retail data), and close the loop on the mobile device. For CTV publishers and FAST (Free Ad-Supported Streaming TV) channels, the RMN opportunity is massive but technically complex. The challenge in CTV is signal loss. IP addresses are unstable, and cookies don't exist. This is where the supply side must lean heavily into clean room interoperability.

  • The Shoppable Video Dream: We are seeing early pilots of "Click to Buy" on CTV, but the immediate value is in measurement.
  • Closed-Loop Measurement: A CTV publisher who can provide log-level data (or clean room access) that allows a retailer to match an ad exposure to a store visit or purchase is infinitely more valuable than one who cannot.

At Red Volcano, we advise CTV apps to ensure their SDKs and SSAI (Server-Side Ad Insertion) setups are capable of passing the necessary parameters that RMNs require for this measurement. If your tech stack strips out the device ID or the content ID, you are breaking the link the retailer needs to prove ROI.

The Role of Supply-Side Intelligence

In this ecosystem, data intelligence is not just for the buyer. The supplier must understand their own value. Using tools like Magma Web or analyzing ads.txt and sellers.json structures allows publishers to see who is buying their inventory and how.

  • Supply Path Optimization (SPO): RMNs are obsessed with efficiency. They do not want to pay a 50% "ad tax" to intermediaries. They want a direct path to the publisher.
  • Direct-to-Publisher Integrations: We are seeing the rise of "Direct Access" deals where large RMNs plug directly into a publisher's header bidder or Prebid server, bypassing traditional reselling chains.

Publishers must audit their own supply paths. If an RMN has to jump through four hops (Reseller A -> Reseller B -> SSP -> Publisher) to buy your inventory, they will likely block you. The path must be clean, transparent, and direct.

A Strategic Action Plan for Publishers and SSPs

To capture the "Off-Site" budget, the supply side needs a proactive roadmap. Waiting for the open market to deliver these bids is a losing strategy.

Phase 1: The Technical Audit (Days 1-30)

  • Identity Resolution: Audit your match rates. What percentage of your traffic can be resolved to a UID2.0, LiveRamp RampID, or ID5 ID? If it is below 20%, you have a problem.
  • Sellers.json Transparency: Ensure your entry in the `sellers.json` file is accurate and marks you as `PUBLISHER` or `INTERMEDIARY` correctly. RMNs script against this file to whitelist supply.
  • MFA check: Ensure you are not flagging as "Made For Advertising" by audit firms like Jounce Media. RMNs often block MFA lists by default.

Phase 2: The Packaging Pivot (Days 31-60)

  • Create "Commerce Packages": Don't just sell "News" or "Sports." Create PMPs specifically designed for retail extension. Bundle your highest viewability slots.
  • Format Innovation: Test a shoppable ad unit. Even if adoption is low, having the capability on your rate card signals innovation to RMN buyers.
  • Data Clean Room Readiness: Even if you don't license Snowflake yourself, ensure your data team understands how to export/import audience segments securely.

Phase 3: The Outreach (Days 61-90)

  • Target the RMNs, not just the Agencies: RMNs have their own media buying teams now. Pitch them directly. Show them why your audience overlaps with their shoppers.
  • Leverage SSPs: If you are a mid-sized publisher, lean on your SSP representatives (Magnite, PubMatic, Index Exchange, etc.). Ask them: "How do I get into your RMN curation packages?"

The Risks: Data Leakage and Dependency

It would be irresponsible not to mention the risks. When a publisher accepts RMN money, they are accepting RMN data. There is a fear of "Data Leakage." If an RMN runs an audience extension campaign on your site, they could theoretically learn which of their users visit your site and then try to target them more cheaply elsewhere. However, the current consensus is that the revenue opportunity outweighs the risk. Furthermore, modern clean room setups allow the publisher to control exactly what data flows back to the buyer. The buyer gets "attribution" (did it work?), not "intelligence" (who are they?). Another risk is dependency. If RMNs become the dominant demand source, they could exert pricing pressure on publishers, treating the open web as a commodity dump. This is why "Premium" positioning is vital. You cannot compete on price against the long tail of the web; you must compete on impact.

Conclusion: The Convergence is Here

The "Third Wave" of advertising is not just about retailers building walled gardens. It is about those walls becoming permeable. RMNs are evolving into massive data-driven demand platforms that desperately need high-quality supply to sustain their growth. For the publisher and the SSP, this is a moment of validation. The open web is not dying; it is becoming the engine room for the largest shift in ad spend in a decade. By focusing on identity resolution, technical transparency, and premium curation, the supply side can move beyond being a passive recipient of ads and become the essential active partner in the retail media ecosystem. The storefront is full; the customers are outside. It is time to invite them in.


Richard is a Senior AdTech Industry Strategist at Red Volcano, specializing in SSP ecosystems and publisher discovery.