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Case study · Email validation API · Worldwide

VeriMailTwo people run an email validation API with 1M+ checks a day and 99.99% uptime, and no ops team

VeriMail is a real-time email validation API that stops sign-ups with disposable and invalid addresses before they reach a customer's database. Many companies check every email through it, more than 1 million checks a day, so for them it is critical infrastructure. I designed the architecture and keep improving it, and I built in the fault tolerance and the backups. That is why one engineer and I run the whole service on 2 to 3 servers, at 99.99% actual uptime against a 99.9% SLA and with p99 latency under 200 ms, with no operations team, where infrastructure this critical usually needs one.

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Client
VeriMail
Product
Real-time email validation API
Customers
Businesses that check every sign-up through it
My role
Fractional CTO
Team
1 engineer and me
Load
1M+ checks a day on 2 to 3 servers
Uptime
99.99% actual against a 99.9% SLA
VeriMail: the product

In numbers

actual uptime against a 99.9% SLA, with two people and no ops team
99.99%
email checks a day from businesses that put every sign-up through it
1M+
average, p99 under 200 ms: fast enough to check as users type
~100 ms
servers carry the whole load, so the service stays cheap to run
2–3
emails validated before they reached a customer's database
50M+
developers build on the API
10K+

The product

A check that runs while the sign-up form submits, the six checks every address passes, and a REST API that answers in under 100 ms. Images from verimail.co.

verimail.co
  • Six checks in order: syntax, mail server, disposable inboxes, blocklists, role addresses, free email providers
  • A simple REST API with a detailed result for every email
01

The starting point

Disposable and fake email addresses fill a product's database with sign-ups that never convert. They burn marketing money and damage the sender's reputation. VeriMail catches them on the sign-up form, before they get in.

Many businesses put VeriMail in front of every sign-up and checkout, so if it slows down or goes down, their sign-ups stop. That makes it critical infrastructure, and it has to hold heavy load and a strict SLA every minute of every day.

02

What we did

  1. The architecture is mine

    I designed the architecture of the whole service and keep improving it: the validation pipeline, the API and the infrastructure under them. It is built so two people can run it and 2 to 3 servers carry the whole load of more than 1 million checks a day, and that keeps the cost of running the service low.

  2. About 100 ms on average, p99 under 200 ms

    Under heavy load the system still answers in about 100 ms on average, and 99% of requests get their answer in under 200 ms. That is fast enough to validate an email while the user is still typing it, so customers add the check to their forms without slowing sign-up down.

  3. 99.99% uptime against a 99.9% SLA

    Customers rely on VeriMail to check every sign-up, so the service runs to a 99.9% uptime SLA and actually delivers 99.99%, a level usually held by companies with a dedicated reliability team.

  4. Fault tolerance and backups

    I built fault tolerance into every layer and set up the backups, so a failure never stops a customer's sign-ups.

  5. Every check a sign-up needs

    Each email goes through RFC syntax, MX records over DNS-over-HTTPS, a database of more than 200,000 disposable domains, blocklists of spam traps and honeypots, and role-account detection, and comes back with a score. Customers can check one address or a whole list in bulk, and bad addresses never reach their database or their marketing budget.

  6. Two people, no ops team

    One engineer and I run the whole service, on modern technology throughout. A service that handles more than 1 million checks a day at this SLA usually needs a team of its own just to keep it up.

03

The result

More than 10,000 developers build on this API and it handles more than 1 million checks a day. It delivers 99.99% uptime against a 99.9% SLA with p99 latency under 200 ms, and two people run it on 2 to 3 servers, where infrastructure this critical usually needs a whole operations team.

oleg.isSent on request

Full case · PDF

VeriMail

Two people run an email validation API with 1M+ checks a day and 99.99% uptime, and no ops team

  1. 01The architecture of the service
  2. 02How it holds heavy load at about 100 ms
  3. 03Fault tolerance and backups
  4. 04The disposable-domain database and how it stays current
  5. 05Running to a 99.9% SLA with two people
  6. 06The stack, and why we chose it
Prepared by Oleg SotnikovPDF

The full VeriMail 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.

I send every case myself and use your email for nothing else.

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