BuiltDiffernt is a revenue engineering firm based in the UK. They design and operate end-to-end pipeline systems for B2B companies, specialising in signal-based outbound that combines messaging, data, and timing to generate attributable pipeline opportunities. Founded by David Sinclair Black.
David Sinclair Black did not build BuiltDiffernt around a channel. He built it around a conviction: that pipeline problems are rarely volume problems. They are design problems.
Fragmented outbound, inconsistent messaging, and disconnected data produce activity without attribution. What Series B+ startups, mid-sized businesses, and enterprise teams need instead are end-to-end systems that combine signal, timing, and precision messaging to generate opportunities that can be traced back to commercial outcomes.
That philosophy shapes everything BuiltDiffernt does. And since early 2023, Smartlead has been the infrastructure layer underneath all of it.
BuiltDiffernt has run 60 to 70 clients entirely through Smartlead. It has used the platform to close £28,900 in a client's first six weeks of outreach. It has built custom API workflows on top of Smartlead that give the firm programmatic control over campaigns that most outbound agencies cannot replicate without stitching together multiple tools.
This is how David built it.
David started in cold email in 2022 and opened his first agency at the end of that year. The channel decision came before the tool decision, and the reasoning was straightforward.
Cold email gave him the ability to reach decision-makers at scale without the budget ceiling of paid advertising or the manual dependency of cold calling. It was automatable, measurable, and not constrained by upfront spend. Within minutes of having the right data and the right copy, he could be generating pipeline from cold traffic.
"Cold email is still the number one for us. And I think for anyone, it will always be. Within a matter of minutes, if you have the right data and the right emails, you can start to generate leads to cold traffic."
He was using Instantly initially, but switched to Smartlead in early 2023 for a specific technical reason: webhook support. BuiltDiffernt was building integrations for clients and needed a sending platform with an API layer serious enough to build on. Smartlead had it. David started using it, and the relationship compounded from there.
"Smartlead was the one I was referred to, and it still is one of the best ones that gets your email in the inbox. You are not going to land in spam. And on top of that, they even teach you how to use the tool and the best practices when it comes to cold email."
BuiltDiffernt's positioning reflects a deliberate move away from the small business end of the outbound market. The firm works with Series B+ funded startups that have proven product-market fit and raised growth capital, mid-sized businesses from 250 employees upward, and enterprise organisations running into the thousands of employees.
What ties these segments together is not industry. BuiltDiffernt works across insurance, IT, tech, and adjacent verticals. What ties them together is a shared problem: sales systems that have not kept pace with how modern B2B buying actually works. Legacy processes, longer cycles, multiple stakeholders, and conversion rates that reflect structural inefficiency rather than a pipeline volume shortfall.
The insight behind this positioning came from the opposite kind of work done earlier. Running outbound for small businesses with short sales cycles teaches you how to make a company sound compelling in cold traffic, how to present it credibly, and where the friction points are that cause prospects to disengage before a conversation starts. David applied that learning to larger organisations and found it worked equally well at contracts that were substantially larger.
Named clients include HPE (Hewlett-Packard Enterprise) and WorldPay, as well as funded growth-stage companies such as Fixer, which David cites as a company that grew significantly from 2024 onward.
When David started, he was not a cold email expert. He was learning the channel at the same time he was building the business on it. That meant every configuration decision, every deliverability choice, and every sequence structure had to be figured out in real time.
What changed that was Smartlead's resource hub. The documentation, blogs, and guides available inside the platform explained not just how to use Smartlead's features, but why the underlying mechanics of cold email work the way they do.
Concepts like spintax were covered not just as a feature but as a deliverability principle, with copy-paste ready syntax. Spam trigger guides pointed directly to the built-in spam checker as the tool to fix the problem being described.
"It not only had this is why you use spintax, but it also had just copy and paste this. It was super, super good and easily integratable."
From the beginning, BuiltDiffernt's delivery model required programmatic control over campaign data. Reporting had to be automated. Lead enrichment had to happen without manual steps. Client notifications had to carry context, not just raw data.
That required a sending platform with an API layer serious enough to build on. Smartlead's API and webhook infrastructure gave David exactly that.
The integrations built in early 2023 became more sophisticated over time, eventually powering real-time Slack notifications with custom variables, automated lead enrichment on positive replies, and subsequence logic triggered by lead behaviour rather than manual input.
"The API is really good. We have some pretty cool backend API stuff. We built out a system where for every interesting response that comes in, it automatically enriches the cold email lead and sends a Slack notification with custom variables that gave our client information about the person they were speaking with."
In B2B outbound, response time is a conversion variable. A lead that replies to a cold email is at peak interest at the moment of reply. Every hour that passes without a response reduces the probability that the conversation becomes a meeting. At scale, across multiple client campaigns running simultaneously, that problem compounds.
Smartlead's Unified Master Inbox gave BuiltDiffernt a single place to manage all inbound replies across clients in real time. David describes the difference in specific terms: an asymmetrical positive difference in meeting conversion rates. Not a marginal improvement. A structural one.
"We noticed an asymmetrical difference, that being a positive difference, in being able to get more meetings for our clients by just being able to respond in real time. A basic answer, but foundationally it has been really necessary for us."
Email deliverability is the constraint that compounds as send volume increases. A campaign that lands in the inbox reliably at 500 emails a week does not automatically do the same at 5,000. Maintaining inbox placement at volume requires more than a warmup tool. It requires granular control over every variable that affects how email providers evaluate sender reputation.
Smartlead gave David that control. The ability to upgrade the warmup pool beyond the default tier, monitor inbox placement through SmartDelivery , and configure send timing down to the randomised-minute level gave BuiltDiffernt deliverability oversight that removed the need for a separate tool entirely.
"This is not really one specific feature, but just more a detailed level of oversight in every aspect of the tool. Warmup, email deliverability placement. It obviously takes away a lot of cost for us because we do not have to use a different tool."
One campaign demonstrates what BuiltDiffernt's system produces when infrastructure, messaging, and lead strategy are aligned. The client was a small design studio in the UK, word-of-mouth reliant, with no prior outreach experience. They engaged BuiltDiffernt in late December and launched a one-month campaign in early January.
The campaign was generating approximately two calls per day, around 40 calls across the month. To sustain that volume, BuiltDiffernt needed roughly four leads per day, sending approximately 30,000 emails per month including automated follow-ups.
By the end of that month, the client had closed a deal worth £18,900. Two weeks later, from the same campaign, a second deal closed at £10,000. Total revenue in the first six weeks: £28,900. The client had no employees and was working to a tight budget. The return was approximately 30 times the agency fee.
"This was a campaign that we ran entirely through Smartlead. And for him, this was a really meaningful result because he had no employees. He was on a tight budget, frankly, and he was able to get a 30x return or something, depending on how much he paid us."
Two Smartlead capabilities were directly responsible for the execution quality. The Unified Master Inbox ensured every positive reply was captured and responded to before the prospect moved on. And Smartlead's webhook infrastructure powered real-time Slack notifications that gave the client contextual information about each incoming lead before picking up the conversation. Not just an alert that someone had replied, but information about who they were and what they were likely looking for.
The feature David is most direct about is the API. In his account, it is not a reporting convenience. It is the layer that makes BuiltDiffernt's delivery model possible at scale. The custom backend systems built on top of Smartlead's API and automation infrastructur automate what would otherwise require manual input at every step: lead enrichment on positive replies, client notifications with lead-specific context, and subsequence logic that triggers on lead behaviour without human intervention.
As the client base grew from a handful of accounts to 60 or 70, that automation layer was what allowed the operation to scale without adding headcount proportionally.
BuiltDiffernt's primary use of the Unified Master Inbox is for clients, not just for its own outreach. Every inbound reply across all campaigns surfaces in one real-time view, giving whoever is managing responses the ability to act on every lead the moment it arrives. David also uses Smartlead's client access feature to extend this directly to clients themselves, letting them log in and manage their own inbound pipeline when appropriate.
Deliverability at volume requires ongoing oversight. Smartlead gives BuiltDiffernt control over the warmup pool tier, access to SmartDelivery for monitoring inbox rate, and the ability to configure send timing to the randomised-minute level. Having all of this inside Smartlead removes the cost and operational overhead of managing a separate deliverability platform. For context on what good deliverability benchmarks look like at scale, Smartlead's cold email response rates guide covers what well-run campaigns can realistically achieve.
As the roster grew, seeing performance across campaigns without running individual reports became a real constraint. Smartlead's global analytics view resolved it.
"The global analytics has gotten a lot better. I love how you could just separate by campaign, separate by client, separate by day, and it will just pull everything up."
David has been in Smartlead's Slack community since 2023 and attended office hours regularly in both 2023 and 2024. His assessment is direct: it is the best community he has used across sequencing tools, and the reason is that it operates at a different level than standard product support. Smartlead University extends that same principle into structured learning, covering deliverability, sequences, and campaign architecture in depth.
Conversations that cover go-to-market campaign design, deliverability strategy, and email account portfolio structure differentiate the Smartlead community from platforms that treat support as a cost centre.
"Some of those elements just really fall down to actually being able to discuss go-to-market campaigns with support, with people that understand it on a technical level. Whether you are a seasoned agency owner or a GTM engineer at an agency and you just want to get some feedback on something."
1. API and Webhooks. The foundational reason David chose Smartlead. Powers real-time Slack notifications with custom lead variables, automated enrichment on positive replies, and the custom backend systems that run BuiltDiffernt's delivery model at scale. Explore Smartlead's API and automation capabilities.
2. Master Inbox. Real-time unified view across all client campaigns. David credits it with an asymmetrical positive difference in meeting conversion rates, the kind of structural improvement that compounds across 60 to 70 active client accounts. Learn more about the Unified Master Inbox.
3. Client Access and White-Labelling. Clients log in and see lead data and campaign reporting in real time without manual exports or reporting calls. Enables a scalable service model where clients can manage their own inbound pipeline when appropriate. Learn more about Smartlead's white-label options.
4. Warmup Pool and Deliverability Controls. Upgradeable warmup pool tiers, inbox placement monitoring through SmartDelivery, and randomised send timing. Detailed oversight that removes the need for a separate deliverability tool. Check your email deliverability with SmartDelivery.
5. Global Analytics. Cross-campaign, cross-client performance in a single dashboard. Filter by client, campaign, or date to pull exactly what is needed for any review or reporting conversation.
6. Community and Support. Slack community and office hours that operate at GTM strategy level, not just ticket resolution. The best community David has used across sequencing tools. Explore Smartlead University.
David's perspective on what Smartlead should continue building reflects the same philosophy that shaped BuiltDiffernt: cold email is the primary channel, and everything valuable that comes next should make cold email more powerful rather than dilute attention across unrelated features.
The feature he returns to is LinkedIn integration. A native or deeply integrated LinkedIn layer, similar to what was briefly available through a previous integration, would allow BuiltDiffernt to run true omnichannel sequences from a single platform rather than managing LinkedIn outreach through a separate tool. He also raises the idea of Meta pixel integration with prospect data from active campaigns, which would allow agencies running paid social alongside cold email to build retargeting audiences directly from Smartlead campaign data.
What he is clearest about is what Smartlead should not do: try to be everything. The value of the platform is that it is built by people who understand email deliverability and outbound execution at depth. That focus is what made it worth building a business on top of. Preserving it matters more than expanding into areas where that expertise does not naturally translate.
"I would not say they need to add loads and loads of features. Cold email is always going to be number one. But anything that complements cold email is always going to be something I will be in favour of, and you have already done this with SmartDialer."
BuiltDiffernt's outbound infrastructure has been built on Smartlead since early 2023. David is clear that this is not inertia. He evaluated alternatives and continues to monitor the market. The reason he has stayed is the compound effect of technical capability, community quality, and support that functions at a level most tools do not reach.
The business that now works with HPE and WorldPay and closes five-figure deals for clients in their first six weeks of outreach was built on that foundation.
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Founder, StackOptimise
Smartlead's combination of automation, unlimited inboxes, and easy campaign management has completely transformed how we run cold email campaigns.
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Founder, Cold Email Hackers
We have about 15 companies and we use Smartlead for all of them.
Founder, DutchSave Media
One of the things I love about using Smartlead is the deliverability feature. If they landed in the bounce or spam folders, we could resolve this quickly.
Co-Founder, Growth Today
I want to continue to use Smartlead to make operations more seamless - the plan is to bring more clients here and build more SOPs.
Founder, FueltoFly
Smartlead listens to the agencies and customers and builds according to what people want, that has really made things easier for us.
Founder, OutboundSync
We build an infrastructure product, and OutboundSync communicates with Smartlead itself. I love the webhook and API. They're really well done and keep getting better.
Founder, Axoleads
With SmartDelivery, you can put all of that in the hands of the tool. It ensures your emails land in inboxes, and by running a simple test, you can see if you're hitting the mark.
Founder, Claygen
Deliverability is the cornerstone of cold email outreach. You could have the best email copy in the world, but if no one is seeing it, it's useless. I really love the feature where you can actually give client accesses to your clients.
Co-Founder, Cymate
I do not want to switch to another software. Pick a solution you trust, stick with it, and keep refining your copy.
CMO, Avalanche Capital
Managing large volumes of emails through multiple inboxes used to be a logistical nightmare. With Smartlead, the process is seamless. We book thousands of discovery calls through cold emails. These campaigns are generating leads at a scale we never thought possible.
Founder, Growth Engine X
We came for the unlimited inboxes, and we stayed for the API. 1.5M cold emails/month, 7,767+ inboxes managed.
Head of Community & Ecosystem, TxtCart
You cannot replace having 10,000 touches with potential clients. When you have that much distribution and reach, you really start to see incredible results. The simplicity of Smartlead made all the difference. It doesn't require you to be a technical wizard.
Founder, Hyperke
Smartlead has been a game-changer for us. It increased our appointment volume, improved ease of use, and offered valuable features. 80% increase in appointments/month, peak of 276 appointments in a single month.
Founder, Kinetyca
Smartlead has been our cold email backbone from day one. The platform evolves constantly, keeping pace with how deliverability and personalization need to work today. 21% overall reply rate, $175K in 4 months for multiple B2B clients.
Founder, Reachflow
Smartlead is centered around deliverability and constantly evolving. Their API is not like any other platform. Smartlead covers all our needs. The focus on core features like deliverability and API integration is unmatched.
CEO, Halfwarm
Our approach to crafting conversational emails led to reply rates that many of my peers thought were unattainable.
Co-Founder, letstrike
We've grown on zero capital, zero marketing, purely cold emailing - and that's the story we love to tell. The best approach is no approach if you can't handle domain meltdown. The second best is something like Smartlead that's built from the ground up for deliverability at scale.
Founder, Fenixtal
Smartlead's white-labeling and automation let us punch above our weight. The 12M euros sales potential? That's what happens when you combine human creativity with Smartlead's precision.
Co-Founder, Digital Creativs
Nine out of 10. Ninety percent of our clients are on Smartlead unless they come in with an existing setup. That's the default.
Co-Founder, BuildingReach
At the end of the day, you have to take a bet on one tool or another. It was a no-brainer taking that bet on Smartlead. We had to even turn down the volume of our marketing campaigns - Smartlead was capable of driving more volume than our sales team was able to fulfill.
Founder & MD, Prospectiv
Since starting the business in January of this year, we've already generated $200K in sales exclusively from cold email. Smartlead has been central to our operations and has exceeded our expectations.
Founder, Growthlynk
There's so much stuff built on top of it. I would be dead if I had to rebuild it with another tool. I can manage hundreds of senders easily. I can send hundreds of thousands of emails.
Founder, Corebits
The platform's HubSpot integration, real-time Slack updates, and advanced campaign customization have been game changers for our business and our clients'.
Founder, Apex Ascension
From day one, we've never used anything else.
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