When most people think about email infrastructure, they usually think about sending emails.

SMTP servers.

Email APIs.

Deliverability.

Tracking.

Automations.

At Keplars , we spend a lot of time thinking about those problems too. But while building an email infrastructure platform, I realized that one of the biggest challenges actually happens before an email is ever sent.

The challenge is simple:

How do you know whether an email address is truly valid?

It sounds like a solved problem. In reality, it is much more complicated than most people realize.

The Problem We Kept Running Into

While building Keplars, we tested and integrated multiple email validation providers.

Most of them offered similar capabilities:

Syntax validation

Domain validation

MX record checks

Disposable email detection

On the surface, the results looked reasonable.

However, when we compared validation results against actual email deliverability and mailbox behavior, we kept seeing inconsistencies.

Some addresses marked as…