Suppressions, Bounces, and Deliverability
Manage your suppression list, understand bounce handling, and protect your sender reputation.
Why It Matters
Sending emails to bad addresses damages your sender reputation. Reputation damage means more of your emails land in spam — not just outreach, but every email your domain sends. Kit’s suppression list and bounce handling protect your reputation by automatically preventing re-contact with addresses that bounced, unsubscribed, or opted out.
Suppression List
The suppression list is account-level — it applies across all campaigns. Navigate to Outreach > Suppressions to view and manage it.
Emails are stored as SHA-256 hashes for privacy. An address gets suppressed automatically when:
- A hard bounce is detected (5xx SMTP error)
- A prospect clicks the unsubscribe link in an outreach email
- A prospect is marked as opted out by your team
- A reply is classified as a bounce by sentiment analysis
You can also manually add email addresses to the suppression list to prevent future contact, or remove an address if it was suppressed in error.
When importing prospects via CSV, Kit checks each email against the suppression list and skips matches automatically.
Bounce Handling
Kit classifies bounces by severity and source:
| Type | SMTP Code | Action |
|---|---|---|
| Hard bounce | 5xx (permanent failure) | Immediate suppression — the address is invalid or doesn’t exist |
| Soft bounce | 4xx (temporary failure) | Retry with backoff — the mailbox may be full or the server temporarily unavailable |
Bounces are detected from three sources:
| Source | How It Works |
|---|---|
| SMTP | The sending server rejects the message at delivery time with an error code |
| DSN | A Delivery Status Notification email arrives after sending (delayed bounce) |
| Sentiment | Kit’s AI classifies a reply as a bounce notification |
Hard bounces suppress the address immediately. Soft bounces are retried, and the message moves to failed status if retries are exhausted.
Unsubscribe Compliance
By default, Kit adds RFC 8058 unsubscribe headers to every outreach email:
- List-Unsubscribe header with a one-click unsubscribe URL
- List-Unsubscribe-Post header for RFC 8058 one-click POST support
- Unsubscribe tokens expire after 6 months for security
You can disable these headers in Outreach > Settings if you’re sending personalized 1:1 cold email where the headers may signal bulk mail to ESPs. The unsubscribe page, suppression list, and opt-out flows continue to work regardless of this setting.
When a prospect clicks unsubscribe, Kit immediately suppresses their email and updates the prospect’s status to unsubscribed. No further emails are sent.
Deliverability Tips
| Practice | Why It Helps |
|---|---|
| Use a dedicated sending domain | Isolates outreach reputation from your primary domain |
| Warm up gradually | Start with 10–15 emails/day and increase over 2–4 weeks |
| Respect the daily cap | Kit limits sending to 50 emails/day — don’t try to work around this |
| Monitor bounce rate | Keep hard bounces below 2% — clean your lists regularly |
| Write relevant emails | Spam complaints drop when prospects recognize why you’re reaching out |
| Include a clear signature | Recipients who can identify the sender are less likely to report spam |
Webhook Events
Kit fires webhook events for key outreach activities. Subscribe to these in Integrations > Webhooks to sync outreach data with external systems.
| Event | Fired When | Payload Model |
|---|---|---|
outreach.prospect.drafted |
AI finishes drafting an email for a prospect | Prospect (ID, campaign_id, company_name, display_name, status) |
outreach.message.approved |
A draft is approved for sending | Message (ID, campaign_id, prospect_id, step_number, subject, status, timestamps) |
outreach.message.sent |
An email is successfully sent via SMTP | Message |
outreach.message.bounced |
An email bounces (hard or soft) | Message (includes last_error_code) |
outreach.message.failed |
Sending fails due to an SMTP error | Message (includes last_error_code, last_error_message) |
All payloads follow the standard webhook envelope. See Webhook Events Reference for envelope format and signature verification.
Note: Prospect and message email addresses are excluded from webhook payloads because they are encrypted at rest.
Quick Checklist
- Review your suppression list at Outreach > Suppressions
- Verify your sending domain has SPF, DKIM, and DMARC records
- Monitor bounce rates — investigate if hard bounces exceed 2%
- Consider a dedicated sending domain for outreach
- Subscribe to outreach webhook events if you integrate with external tools
Next Steps
- Setting Up Email Delivery — SMTP and IMAP configuration
- Webhook Events Reference — full payload documentation for all event types
- MCP Tools Reference — manage outreach programmatically via AI assistants