Catch-all domain

A domain whose mail server accepts mail for any address, so a check before sending cannot tell whether a mailbox really exists.

Address verifiers ask the receiving server about a mailbox without sending a message (an SMTP RCPT TO check). A catch-all server says yes to every address, real or not, and may bounce or quietly drop the message later. Addresses at such domains are neither valid nor invalid: they are unknown, and a verifier should report them that way.

Share: LinkedIn · X ·

Related terms

Hard bounce: A permanent delivery failure: the address or its domain does not exist or refuses mail.
MX record: A DNS record that names the mail servers accepting email for a domain, each with a preference number: lower numbers are tried first.
Spam trap: An email address no real person uses, kept by a mailbox provider or a blocklist operator to catch senders with poor list practices.

← All terms

Need this built, fixed or reviewed?

I build and rescue products with AI coding agents under rules: AI features in production, honest estimates, email that gets delivered.

Book a free 30-min call See price and start date

How I work

Przemysław Zalewski · 15+ years shipping software

“a true bias for action” client CTO, public LinkedIn recommendation

Confidential by default. NDA is standard. I never show your project, name or screenshots without written consent, which is why this site names no clients without permission.
Your code, your accounts. Code and data stay in your repository and accounts. AI tools run with training on your data turned off, and secrets never reach a model.
A handover you can use. Every project ends with the same checklist: a README that gets it running, one architecture diagram, written decisions, CI, a runbook and a recorded walkthrough. It is done when someone outside the project can run it from the docs.
Boring technology where it counts. I pick a stack you can hire for. Anything experimental needs your yes and an exit plan.
Approach matched to your risk appetite. Prototype, product or regulated: the level decides how much autonomy the agents get and how much review and validation each change needs.
Everything checkable. Every number on my pages links to its source. My tools are free, and the idea validator skill is open source (MIT).

All principles and risk levels →