When I started building findmemail.io , I made one architectural decision early: never return an email we haven't SMTP-verified at request time. No pattern guessing, no domain-only validation. This post is about how that constraint shaped the system.

Why SMTP verification at request time

Most B2B email finders do verification asynchronously, in batches. The result is a database where some entries are verified, some are stale, some never were. Users don't know which is which.

This kills cold email deliverability. A 5% bounce rate flags your sender domain. A 30% bounce rate (common with mixed-quality data) burns it.

The constraint at findmemail.io: every email returned to the user has been SMTP-probed in the last 7 days.…