- Relay emails through your existing Postfix or other SMTP infrastructure
- Receive full event visibility in SendPost (processed, sent, delivered, bounces, opens, clicks, unsubscribes)
- Apply SendPost’s per-provider throttling (27 ISP categories), IP pool routing, and retry logic
- View all email analytics in one centralized dashboard alongside other providers
sp-bounce.{domain}) are reused. SendPost prepares each message (DKIM, tracking pixel, click rewrites, headers) and relays it over SMTP to your server. Delivery events are captured via synchronous SMTP responses, SendPost tracking, the existing bounce processor, and an optional event reporting agent you install on your MTA.
Why Use Custom SMTP with SendPost?
| Feature | Your SMTP Alone | Custom SMTP + SendPost |
|---|---|---|
| Unified dashboard | ❌ | ✅ All events in one place |
| Per-ISP throttling | Manual | ✅ Gmail, Yahoo, etc. (27 categories) |
| IP pool routing | ❌ | ✅ Route % traffic through your MTA |
| Retry & failover | Custom | ✅ Built-in retry logic, fallback to other providers |
| Open/click tracking | Custom | ✅ SendPost tracking endpoints |
| Bounce processing | Custom | ✅ Reuses SendPost bounce infrastructure |
| Gradual migration | ❌ | ✅ Compare your MTA vs SendPost IPs side by side |
What’s Covered in This Guide
Setting Up
Create a Custom SMTP TPSP, verify connectivity, and install the event reporting agent
Sending Emails
Send emails through your SMTP server using the SendPost API with IP Pool routing
Event Reporting Agent
Install and configure the agent to report delivered, bounced, and deferred events from your MTA logs
Event Types
Understand CS event types and how they map to the sending lifecycle
Analytics
Track opens, clicks, bounces, and configure rate limiting
Troubleshooting
Common issues, FAQs, and getting help
Quick Reference
Key Endpoints
| Purpose | URL |
|---|---|
| Send Email | POST /api/v1/subaccount/email/ |
| Event Ingestion (agent) | POST https://events.sendpost.io/api/v1/tpsp/custom-smtp/events |
| View Events | SendPost Dashboard → Events |
Setup Checklist
Create Custom SMTP TPSP
In SendPost: Providers → NEW → Custom SMTP. Enter host, port, security, auth, and max rate.
Copy Event Ingestion API Key
Save the API key shown once after creation; it authenticates the event reporting agent.
Install Event Reporting Agent
Run the one-liner install on your MTA server (Postfix supported initially).