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Overview

Unosend automatically validates every email address before sending. Risky addresses — spam traps, disposable emails, invalid mailboxes — are suppressed to protect your sender reputation and keep bounce rates low. Suppression is automatic: you don’t need to configure anything. Every email sent through the API, SMTP, or broadcasts passes through the suppression engine.
Contact suppression is free on all plans — no extra cost for validation or filtering.

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What Gets Suppressed

Unosend checks every email address through multiple validation layers:
CheckWhat It CatchesExample
SyntaxMalformed email addressesuser@, @domain.com
Typo DetectionCommon domain misspellingsuser@gmial.com → suggests gmail.com
Disposable DomainsTemporary email servicestest@tempmail.com, user@guerrillamail.com
Spam TrapsKnown spam trap patternshoneypot@, spamtrap@
Role-BasedGeneric addresses (flagged, not blocked)info@, support@, noreply@
MX RecordsDomains without mail serversuser@nonexistent-domain.xyz
SMTP VerificationMailboxes that don’t existRCPT TO check against mail server
Previous BouncesAddresses that hard bounced beforeAutomatically suppressed after bounce
Spam ComplaintsRecipients who reported spamAutomatically suppressed
UnsubscribesContacts who unsubscribedAutomatically honored
Checks run in order — if an address fails an early check, later checks are skipped for speed.

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Suppression Reasons

When an email is suppressed, you’ll see one of these reasons in the API response or dashboard:
ReasonDescription
invalid_syntaxEmail format is invalid
no_mx_recordsDomain has no mail servers
disposableTemporary/throwaway email service
spam_trapMatches known spam trap patterns
typo_domainDomain appears to be a typo
mailbox_not_foundSMTP verification says mailbox doesn’t exist
hard_bouncePreviously bounced with a permanent error
spam_complaintRecipient previously reported spam
unsubscribeContact unsubscribed
manualYou manually added the address to your suppression list

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How It Works in Practice

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Transactional Emails (API & SMTP)

When you send an email via the API or SMTP:
  1. The recipient address is validated
  2. If suppressed, the API returns a 422 error with the reason
  3. If valid, the email is queued and sent

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Broadcasts

When sending a broadcast to an audience:
  1. All recipient addresses are validated in bulk
  2. Suppressed contacts are skipped automatically
  3. Only valid contacts receive the broadcast
  4. The broadcast analytics show suppressed count separately

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Contact Import

When importing contacts via CSV:
  1. Each email is validated during import
  2. Invalid addresses are flagged but still imported
  3. You can review and remove flagged contacts before sending

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Managing Your Suppression List

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View Suppressions

Go to Suppressions in the dashboard to see all suppressed addresses for your organization, with reasons and timestamps.

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Manually Suppress an Address

Add an address to your suppression list to prevent all future sends: 
curl -X POST https://www.unosend.co/api/v1/suppressions \
  -H "Authorization: Bearer un_xxxxxxxxxx" \
  -H "Content-Type: application/json" \
  -d '{
    "email": "user@example.com",
    "reason": "manual"
  }'

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Remove a Suppression

If an address was incorrectly suppressed, you can remove it:
cURL
curl -X DELETE https://www.unosend.co/api/v1/suppressions/supp_abc123 \
  -H "Authorization: Bearer un_xxxxxxxxxx"
Only remove suppressions if you’re confident the address is valid. Re-sending to previously bounced addresses can damage your sender reputation.

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Validate Emails Before Sending

Use the validation API to check addresses without sending:
cURL
curl "https://www.unosend.co/api/v1/validation?email=user@example.com" \
  -H "Authorization: Bearer un_xxxxxxxxxx"
200
{
  "data": {
    "email": "user@example.com",
    "valid": true,
    "score": 95,
    "details": {
      "syntax_valid": true,
      "mx_valid": true,
      "is_disposable": false,
      "is_spam_trap": false,
      "is_role_based": false
    }
  }
}
The score field (0–100) indicates deliverability confidence. Scores above 80 are considered safe to send.

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Domain Typo Corrections

Unosend automatically detects and blocks common domain typos:
TypedLikely Meant
gmial.comgmail.com
gmal.comgmail.com
hotmal.comhotmail.com
yaho.comyahoo.com
outlok.comoutlook.com
Emails to typo domains are suppressed with the typo_domain reason.

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Bounce Rate Protection

Unosend monitors your bounce rate and takes action to protect your sender reputation:
  • Threshold: 5% bounce rate over 100+ emails in 24 hours
  • Action: Account is automatically suspended
  • Recovery: Contact support to review and resolve
Use Email Validation to clean your contact list before sending large campaigns. This prevents bounce spikes and keeps your account in good standing.

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Best Practices

Run bulk validation when importing contacts. It’s much easier to clean a list upfront than to deal with bounces after sending.
Check suppressions weekly. A sudden spike in disposable or invalid addresses may indicate a bot attack on your signup form.
Hard bounce suppressions exist for a reason. Re-sending to bounced addresses will increase your bounce rate and may trigger suspension.
Require email verification on signup to ensure contacts are valid before they enter your audience. This dramatically reduces bounces.

Email Validation Guide

Validate email lists in bulk

Suppressions API

Full API reference for suppressions