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SendPost’s Custom SMTP integration allows you to use your own SMTP server as a Third-Party Sending Provider (TPSP). This means you can:
  • 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
No DNS changes are required. Your existing verified domain and bounce handling (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.

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Why Use Custom SMTP with SendPost?

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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

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Quick Reference

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Key Endpoints

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Setup Checklist

1

Create Custom SMTP TPSP

In SendPost: Providers → NEW → Custom SMTP. Enter host, port, security, auth, and max rate.
2

Copy Event Ingestion API Key

Save the API key shown once after creation; it authenticates the event reporting agent.
3

Install Event Reporting Agent

Run the one-liner install on your MTA server (Postfix supported initially).
4

Configure IP Pool

Create an IP Pool in SendPost that routes traffic to your Custom SMTP TPSP.
5

Whitelist Domain

Use the same verified sending domain in SendPost that your MTA uses.
6

Send Test

Use the “Send Test” button in the UI or API with the IP pool to confirm the full pipeline.