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.

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23% of B2B domains are catch-all
3-probe fingerprinting
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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

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