# How Catch-All Validation Works in Practice

Catch-all validation in CSVgo is a **second-stage verification process** applied only to emails that could not be confirmed during standard verification.

This page explains what happens to a catch-all email after it is detected and how CSVgo determines whether it is deliverable, undeliverable, or remains risky.

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### When Catch-All Validation Is Triggered

Catch-all validation starts only after primary email verification.

An email enters catch-all validation if:

* The domain accepts all mail
* SMTP responses do not confirm mailbox existence
* The email is neither clearly valid nor clearly invalid

Only these emails go through this step.

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### Step 1: Catch-All Detection

CSVgo first confirms that the domain behaves as a catch-all domain.

This means:

* The mail server responds positively to arbitrary addresses
* Mailbox-level existence cannot be verified directly

At this point, the email is marked as **catch-all**, not deliverable.

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### Step 2: Signal Collection

CSVgo evaluates additional signals beyond basic SMTP responses.

These signals focus on:

* Mail server behavior patterns
* Domain-level configuration characteristics
* Routing and response consistency
* Known behaviors of protected or proxied email environments

No single signal determines the result.

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### Step 3: Signal Correlation and Confidence Scoring

Collected signals are evaluated together to determine confidence.

In practice:

* Strong positive signal combinations increase confidence
* Strong negative signal combinations decrease confidence
* Inconsistent or weak signals reduce confidence

This avoids decisions based on a single unreliable indicator.

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### Step 4: Conservative Classification

Based on signal confidence, CSVgo assigns one of three outcomes:

* **Deliverable**\
  There is sufficient evidence that the mailbox can receive email.
* **Undeliverable**\
  There is sufficient evidence that the mailbox will not accept email.
* **Risky**\
  There is not enough reliable information to make a confident decision.

Emails remain marked as risky only when uncertainty cannot be reduced safely.

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### What CSVgo Does Not Do

To avoid false results, CSVgo does not:

* Assume all catch-all emails are valid
* Automatically discard all catch-all emails
* Rely on a single SMTP response
* Send real emails as a verification shortcut

This prevents misleading classifications.

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### Why Some Emails Remain Risky

Some email environments intentionally limit verification signals.

This can happen when:

* Security layers suppress responses
* Servers return generic or inconsistent replies
* Mailbox-level data is inaccessible externally

In these cases, keeping the email marked as risky is the most accurate outcome.

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### How This Helps Outbound Teams

This process:

* Reduces the size of the risky bucket
* Recovers deliverable inboxes
* Preserves transparency for uncertain cases
* Allows informed sending decisions

Teams can then choose to:

* Send to deliverable catch-alls confidently
* Test risky emails at low volume
* Exclude them entirely

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### Summary

In practice, catch-all validation in CSVgo:

* Applies only to uncertain emails
* Evaluates multiple signals together
* Uses conservative decision logic
* Reduces uncertainty without hiding risk

This step turns catch-all handling from guesswork into a controlled decision process.