Understanding Validation Results

After MailCop validates an email address, you’ll receive a clear status indicating whether it’s safe to send to. Here’s what each result means and how to act on it.

Email Statuses

Good ✓

The email address is valid and deliverable. Our checks confirmed:

The email format is correct
The domain exists and has mail servers
(For SMTP validation) The specific mailbox exists

Action: Safe to include in your campaigns.

Bad ✗

The email address has problems and will likely bounce. Common reasons include:

Invalid email format (missing @ symbol, typos)
Domain doesn’t exist
Domain has no mail servers configured
(For SMTP validation) The specific mailbox doesn’t exist
Address matched one of your filters

Action: Remove from your list. Sending to these addresses will hurt your sender reputation.

Pending ⏳

The email is still being validated. This status is temporary and will change to Good or Bad once processing completes.

Action: Wait for validation to complete.

API Response Fields

When using the API, you’ll receive detailed information about each validation:

{
  "email": "[email protected]",
  "status": "good",
  "validation_type": "smtp",
  "role_account": false,
  "free_provider": false,
  "catch_all_domain": null,
  "result": {
    "domain": "example.com",
    "checks": { "filter": "pass", "disposable": "pass", "format": "pass", "mx": "pass", "smtp": "pass" },
    "smtp": null
  },
  "credits_used": 10
}

Response fields explained

Field	Description
`email`	The email address that was validated
`status`	Result: `good`, `bad`, or `pending`
`validation_type`	Method used: `mx` or `smtp`
`credits_used`	Number of credits charged
`reason`	Why it failed, as readable text (only for bad emails)
`reason_code`	Why it failed, as a stable code (only for bad emails)
`result.checks`	Which checks passed, failed or were skipped
`role_account`	Address is a role mailbox like `info@`
`free_provider`	Address is on a free provider like Gmail
`catch_all_domain`	The domain accepts any mailbox, so a good result cannot confirm this one exists (when requested)

See the Verify Endpoint for every field.

Failure Reasons

When an email is marked as bad, the reason_code field explains why:

`reason_code`	Meaning
`invalid_format`	Email doesn’t match proper format
`no_mx_records`	Domain doesn’t exist or has no mail server configured
`mailbox_not_found`	Specific email address doesn’t exist (SMTP only)
`mailbox_full`	Recipient’s mailbox is full (SMTP only)
`smtp_rejected`	Mail server refused the check (SMTP only)
`smtp_unreachable`	Mail server could not be reached (SMTP only)
`blocked_by_filter`	Matched one of your blocklist filters
`disposable_domain`	Domain is a known temporary email service
`validation_failed`	Bulk lists only: validation errored repeatedly and the email was marked bad

Interpreting Results for Your Use Case

For email marketing

Focus on the good emails only. Even a small percentage of bad emails can:

Increase bounce rates
Damage sender reputation
Get you flagged by email providers

Recommended: Download the “Good emails only” export and use that for your campaign.

Use real-time API validation to catch bad emails before they enter your system:

// Example: Validate on form submit
const result = await validateEmail(userEmail);
if (result.status === 'bad') {
  showError('Please enter a valid email address');
}

For CRM hygiene

Regularly validate your contact database to:

Remove addresses that have gone stale
Identify domains that no longer exist
Clean up typos and formatting issues

Accuracy Expectations

No email validation is 100% accurate. Here’s what to expect:

MX Validation accuracy

Catches: Invalid formats, non-existent domains, missing mail servers
Misses: Individual mailbox issues, full inboxes, disabled accounts
Typical accuracy: 85-90% of bad emails detected

SMTP Validation accuracy

Catches: All of the above, plus non-existent mailboxes
Misses: Catch-all servers (accept any address), temporary issues
Typical accuracy: 95-98% of bad emails detected

Why 100% isn’t possible

Some mail servers are configured to accept all addresses (catch-all). Others temporarily go offline. And email addresses can become invalid after validation. For best results:

Validate close to when you’ll send
Use SMTP validation for important campaigns
Monitor your actual bounce rates and re-validate periodically

Working with Filtered Emails

If you’ve set up filters, some emails may be marked as bad because they matched your blocklist rather than failing validation.

The reason field will show blocked_by_filter for these addresses. This helps you:

See which of your filters are being triggered
Identify patterns you might want to block
Audit your filtering rules

Next Steps

Learn about validation types to choose the right method
Set up filters to automatically block unwanted addresses
Use the API for real-time validation