Catch-All Email Checker - Identify Risky Domains | BounceZero
3-Probe SMTP Detection

Catch-All Email Checker Know What Accepts Everything

Catch-all domains accept email for every address - real or invented. Standard verification can't detect this. BounceZero uses a 3-probe SMTP method to fingerprint catch-all behavior and score the delivery risk accurately.

A catch-all email checker tests whether a domain's mail server accepts every address, which makes a normal validity check meaningless for that domain. In the BounceZero corpus of April to October 2026, 2.3% of non-freemail (business and ISP) addresses sat on catch-all domains, rising to 12.4% on .org domains, so the checker tells you which addresses can only be confirmed by a careful send.

Try Free - 100 Credits Try Demo Tool
23% of B2B domains are catch-all
3-probe fingerprinting
No credit card required 100 free verifications/month GDPR compliant

Backed by & listed on

G2
G2
Listed
aws
AWS
Activate
Google
for Startups
NVIDIA Inception Program
NVIDIA
Inception
MongoDB
Atlas
Gartner
Gartner
Peer Insights
Product Hunt
Featured
RapidAPI
Marketplace
Datadog
Startup Program
UK Ltd Co.
No. 17153835
G2
G2
Listed
aws
AWS
Activate
Google
for Startups
NVIDIA Inception Program
NVIDIA
Inception
MongoDB
Atlas
Gartner
Gartner
Peer Insights
Product Hunt
Featured
RapidAPI
Marketplace
Datadog
Startup Program
UK Ltd Co.
No. 17153835

What is a Catch-All Domain?

A catch-all (or accept-all) domain is configured to accept email for every address at that domain - whether the mailbox exists or not. The server returns a "250 OK" to any RCPT TO command, regardless of whether the user exists.

This makes standard single-probe SMTP verification unreliable. A server might accept [email protected] and [email protected] with the exact same response.

BounceZero detects this by sending 3 probes with invented addresses. If all are accepted, the domain is flagged as catch-all and classified as Risky.

The Catch-All Problem

23% of B2B corporate domains are catch-all. Sending to these without detection means your bounce rate won't reflect the true picture - until the provider starts penalizing your domain.

23%
of B2B domains are catch-all
3 probes
BounceZero uses to fingerprint catch-all behavior

How BounceZero's 3-Probe Detection Works

A single SMTP probe can't detect catch-all. BounceZero runs three probes with invented random addresses to fingerprint the server's behavior.

1

Probe 1 - Invented Address

BounceZero sends an SMTP RCPT TO for a random invented username at the target domain (e.g., [email protected]). If the server accepts it, catch-all is suspected.

2

Probe 2 - Second Random Address

A second invented address is tested. Both accepted? Catch-all confidence rises significantly. The server has now accepted two non-existent mailboxes.

3

Probe 3 - Confirmation

A third probe confirms the pattern. If all three invented addresses are accepted, the domain is classified as catch-all with high confidence. BounceZero marks the result as Risky.

What happens with the result?

Catch-all addresses are classified as Risky rather than Valid or Invalid. BounceZero provides a confidence score and detailed reasoning to help you decide whether to include them in your campaign based on your risk tolerance.

Frequently Asked Questions

Related Verification Tools

Disposable Checker

Block 800+ throwaway email providers at sign-up with real-time detection.
Deliverability Test

Check SPF, DKIM, DMARC, blacklists, and sender reputation in one scan.
Spam Trap Checker

Detect pristine, recycled, and typo-based spam traps before you send.
Bulk Validation

Upload a dashboard job of up to 1,000,000 addresses.
Catch-All Detection Guide

Interpret accept-all results, risk, and campaign handling.
Catch-All Campaign Strategy

Decide how to segment and send to accept-all domains.

Detect Catch-All Domains Before You Send

100 free verifications every month. No credit card required.

Start Free

Catch-all domains on lead lists

Catch-all behaviour is concentrated in a few places: 12.4% of .org domains, 24.7% of AOL addresses and 27.7% of Yahoo addresses in the BounceZero corpus of April to October 2026, against 2.3% across non-freemail (business and ISP) domains (Lead List Quality Benchmarks 2026). Finder tools count those addresses as found; a checker tells you they are unconfirmed.

What is a catch-all lead?

Why finders mark them valid and verifiers do not

.org addresses on lead lists

The highest catch-all share of any segment

Yahoo addresses on lead lists

Catch-all and throttled probes at one provider

Email finder guide

How finders guess addresses and where catch-all breaks them

Free tools & checkers

Single-email checks, no signup required

Free bulk email verifier

Verify a whole list up to your free monthly credits

SMTP email checker

See exactly what an MX server says

Disposable email checker

Spot 10minutemail-class temp addresses

Spam trap checker

Identify pristine + recycled traps

Email deliverability test

Full authentication + spam-score check

Header analyzer

Decode the Received chain and trace the path

Continue through related topics

Free email tools Email verification guide Email deliverability hub

Follow BounceZero

LinkedIn
Follow us

Ready for bulk verification?

Verify Thousands - Same Up to 99.8% accuracy in internal testing on SMTP-verifiable addresses

Upload a CSV, get clean results in minutes. $3 per 1,000 emails. Credits never expire. No subscription.

Get 100 Free Credits View pricing

No credit card required  -  100 free verifications every month  -  Full 5-stage pipeline