B2B Email Validation: what happens when you query an SMTP server

Whassup?! The Sound of Our Email Validator

Over the past few months, one of the trickiest technical challenges we’ve tackled has been building our very own Email Validator – to make our database more reliable than ever.

Of course, we’ve been checking email addresses for a long time (selling B2B databases without validating emails is reckless and can land buyers in serious blacklisting trouble – always make sure addresses are valid!). Until recently, we relied on solid existing tools. There are plenty of them, some excellent, and we even built great collaborations with a few. But we noticed some inconsistencies and inaccuracies that pushed us to invest both brainpower and budget into developing a modern, safe, and fully functional tool that gives us solid, reliable answers.

Creating a tool like this means getting your hands dirty.
No skimming the surface here: you have to dive into the complex workings of mail servers and protocols – without getting lost along the way.

At the heart of validation is the dialogue with the recipient’s server. To explain it simply, we like to use an analogy everyone familiar with classic American pop culture will get: the legendary “Whassup?!” phone call.

Because validating an email is a bit like calling your friends in that famous ad: you try, you wait, and sometimes the answer is exactly what you expect… sometimes it’s completely unexpected.

And that’s exactly what our Email Validator does: it “rings” the domains, and depending on the response, it figures out what’s really behind the address.

Case 1: Missing MX

You arrive at the building, ready to ring… but there’s no intercom!
Maybe there was one before, but now, nothing.
You leave, promising to come back someday to see if it’s been installed.

Case 2: Temporary / Disposable Email

You ring: “Is Duke here?”
A robotic voice replies: “Yes, of course!”
You’re not convinced. You leave, probably never coming back — though you still note the address.
You mutter to yourself: “Whassup with that?!”

Case 3: Catch-All

You ring: “Is Kevin here?”
– “Yes, he is!”
You ring for Jerry:
– “Yep, him too!”
Brad?
– “Of course!”
Carl?
– “Everyone’s here!”
You smile and walk away – if they say yes to everyone, they’re clearly faking it.
“Dude… seriously?”

Case 4: Greylisting

“Is Duke here?”
– “I’m not sure, try again in 15 minutes.”
You come back later, hoping Duke will have appeared.
“Whassup… come on!”

Case 5: Timeout

You ring. Silence.
Maybe they’re asleep, the line is down, or the intercom is broken.
You’ll try again another day.
“Whassup, hello?”

Case 6: Sender Rejected

You introduce yourself: “Hi, it’s Andrea from Bancomail…”
– “No thanks, we don’t need anything!”
Conversation over. Maybe you’ll come back under a different name someday.
“Whassup, man?”

Case 7: SMTP Rejected

You ring: “Is Jerry here?”
– “Jerry who?”
You explain: “Jerry Smith…”
– “Never heard of him.”
A bit disappointing, but at least they were honest.
“Dude… fair enough.”

Case 8: Valid Email

You ring: “Is Kevin here?”
– “Yes, this is Kevin!”
They answer sincerely. You asked about others too, and they replied honestly.
You leave reassured – finally, a real answer.
“Whassup! Finally!”

In summary:
Validating emails is basically a tour of digital intercoms, in true “Whassup?!” style — some people aren’t there, some pretend to be, some are unsure, some ignore you… and occasionally, someone answers.

We do this thousands of times a day, politely, punctually, and with an algorithm that never misses.

Because even in the digital world, the old rule of apartment buildings still applies:

If nobody answers, don’t insist.
But if everyone opens the door too eagerly, maybe think twice.

PS:
Thanks to everyone who read to the end – we hoped to bring a smile to a usually serious topic.
And a special nod to Duke, Kevin, Jerry, Brad, and Carl – and to everyone who remembers the classic “Whassup?!” ad.