How to integrate custom routing with ESP tracking?

Combining custom mail routing with ESP tracking features requires thoughtful architecture to maintain both control and visibility.

Approach 1: ESP as smart host

Your application generates messages

Messages route through your MTA to ESP

ESP wraps links, adds tracking pixel, handles analytics

ESP delivers to recipients

You get ESP tracking with your origination point

Approach 2: API injection for tracking only

Generate content via ESP API to get tracked links/pixels

Receive the modified content back

Send through your own MTA

Track pixels/links point to ESP servers for data collection

Approach 3: Self-hosted tracking

Implement your own click/open tracking

Full control but no ESP features

Host tracking endpoints on your infrastructure

Build analytics yourself

Considerations:

ESP tracking domains need to be trusted (custom tracking domains help)

Authentication must work for final delivery path

Reporting may be split between systems

Cost model changes (may pay for tracking without using ESP delivery)

Some ESPs support these hybrid models better than others. Discuss your architecture with ESP support before committing to a design.