Email verification 101

Valid, invalid, catch-all, unknown — explained.

This guide is part of the CorrectInbox knowledge base. The full article content is populated from our CMS in production; the page structure and styling here are final.

The short version

CorrectInbox specializes in resolving catch-all Microsoft 365 and Google Workspace domains accurately — and returning a confidence score instead of a blind guess when an address genuinely can't be resolved.

How CorrectInbox handles it

Our verification engine combines syntax, MX, and SMTP signals with a dedicated catch-all resolver. Results map to four honest states: valid, invalid, catch-all, and unknown — each with a confidence score you can threshold against your own risk tolerance.