Case study · Cold email and outbound sales
LeadTrainA team of three built LeadTrain, a cold email platform that now sends more than 20 million emails a month
LeadTrain runs cold outbound end to end: it finds the buyers, buys and configures the sending domains, creates and warms the mailboxes, gives every sender a profile and a site, sends multi-step campaigns and sorts every reply. As fractional CTO and startup advisor, I designed the whole architecture and built the product with two more people. It now sends more than 20 million emails a month and is built to keep deliverability above 60%.
- Client
- LeadTrain
- Product
- Full-cycle cold email
- Volume
- 20M+ emails a month
- Model
- Credits, from $249 a month
- My role
- Fractional CTO and startup advisor
- Team
- Me and two more people
- Website
- leadtrain.app
In numbers
- emails sent every month
- 20M+
- deliverability, the level the system is built to keep
- 60%+
- people built the product, me included
- 3
- for a new mailbox to climb from 5 emails a day to 1,000, with no one touching it
- 30 days
- labels the AI puts on every reply, with interested buyers first
- 9
- Google Workspace or Outlook seats to buy: senders, domains and DNS are set up automatically
- 0
The product
The public site: the inbox where every reply arrives labelled, a domain with its DNS records written and kept correct, a mailbox warming up from 5 emails a day to 1,000, and campaign results per step and per version. The product screens use sample data.
The starting point
Cold email works only when it reaches the inbox, and getting there usually takes six separate tools: a contact database, a registrar with its DNS panel, mailbox seats, a warm-up service, a sending tool and an inbox. None of them knows what the others do, and much of the mail ends up in spam. LeadTrain set out to replace that whole stack with one system tuned for one result: more emails in the inbox and more replies from buyers.
I joined as fractional CTO and startup advisor, designed the whole architecture and built the product with two more people. The team had no separate infrastructure, deliverability or QA staff, so the architecture had to cover that work.
What we did
Deliverability above 60%, by design
Each workspace sends through its own isolated sending account, so one customer's reputation never touches another's. Every address is verified before the send, mail goes out in the recipient's working hours spread across the mailboxes, and a campaign pauses itself if bounces reach 5% or complaints 0.1%.
Domains and mailboxes that set up and warm themselves
LeadTrain buys sending domains next to the customer's brand, writes the SPF, DKIM, DMARC and MX records and keeps them correct, so the main domain never sends cold mail. It creates the mailboxes itself, with no seats to buy, and warms each one automatically from 5 emails a day to 1,000 by day 30 while the customer writes the sequence.
Sender profiles, avatars and sites, generated
A buyer who gets a cold email checks who sent it. LeadTrain generates the senders' avatars and profiles and builds the websites behind the sending domains automatically, so every sender has a consistent presence. Agencies do this by hand, domain by domain.
Multi-step campaigns with A/B testing built in
A campaign has as many steps as it needs, with delays, send windows and personalisation, and the AI can draft the whole sequence from a short description. Any step can carry several versions, and the built-in A/B testing shows which subject line and body get answered, so the campaign keeps the winner and drops the rest. Delivery results also feed into that optimisation.
Every reply sorted, every email tracked
AI reads each reply and gives it one of nine labels. Interested replies come first in one inbox across every mailbox and campaign, an out-of-office pauses that person's sequence, and a yes or a no stops the follow-ups, so no buyer gets step 3 after answering. I designed custom tracking that follows every email through sent, delivered, opened and replied, per step and per version.
Hooks and integration with the customer's product
LeadTrain plugs into the customer's own systems: webhooks report every event, the API and integrations connect it to the product and the CRM, and leads come in from Apollo's B2B database with verified emails only.
20 million emails a month on a team of three
I designed the architecture so that a small team could build and run what a large company would staff a whole department for.
The result
A team of three, with me as fractional CTO and startup advisor, built a cold email platform that covers the whole cycle: buyers found, domains bought and configured, mailboxes warmed, sender profiles and sites generated, campaigns sent and tested, replies sorted. It sends more than 20 million emails a month with deliverability above 60%.
Full case · PDF
LeadTrain
A team of three built LeadTrain, a cold email platform that now sends more than 20 million emails a month
- 01The architecture: domains, mailboxes, warm-up, sending and the inbox
- 02How deliverability stays above 60%: isolation, verification, auto-pause
- 03Generated sender profiles, avatars and sites
- 04A/B testing, delivery optimisation and per-step tracking
- 05Hooks, the API and integration with the customer's product
- 06How three people built a system that sends 20M+ emails a month
The full LeadTrain case
The public story stops here. The PDF has the rest: the architecture before and after, the migration plan, how the team works with AI agents, what it all costs to run and where the savings came from.
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