# Custom SMTP Integration — PostFrame — EternalEngine

Connect any standard SMTP server to PostFrame. Use your own mail infrastructure with full tracking and analytics.

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Provider Integration

# Custom SMTP

Point PostFrame at any server that speaks SMTP — Postfix, Exchange, a hosted relay — with STARTTLS on 587 or TLS on 465. Link and open tracking still work, because PostFrame rewrites the message before it hands it over.

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## Why Custom SMTP

Universal compatibility

Works with any server that speaks SMTP — Postfix, Exchange, Zimbra, or hosted SMTP

Tracking kept

Links are rewritten and the open pixel added before the message reaches your server, so analytics match every other provider

On-premise support

Connect mail servers behind your firewall with outbound SMTP relay

STARTTLS or TLS

Port 465 uses implicit TLS; any other port negotiates STARTTLS — you pick the port, PostFrame picks the mode

Ideal For

On-premise infrastructure

Companies with existing mail servers they need to keep

Niche providers

Connect any SMTP-compatible service not in our native integration list

Hybrid setups

Mix custom SMTP with managed providers for failover

Regulated industries

Healthcare and finance where mail must route through approved infrastructure

## Keep exploring PostFrame

[### Amazon SES Bring your own AWS account and region. Open Amazon SES →](https://eternalengineos.io/features/postframe/byop/amazon-ses/)[### Postmark Transactional-first provider connected with one token. Open Postmark →](https://eternalengineos.io/features/postframe/byop/postmark/)[### Isolated providers Credentials, priority and limits are per workspace. Open Isolated providers →](https://eternalengineos.io/features/postframe/multi-tenant/isolated-providers/)

Questions

## Common questions, straight answers.

What details does a custom SMTP connection need?

Host, port, username and password. Port 465 uses implicit TLS; other ports use STARTTLS. PostFrame stores the credentials in its secrets vault.

Does tracking still work through my own SMTP server?

Yes. PostFrame rewrites links into tracked redirects and adds the open pixel before the message is handed to your server, so opens and clicks report exactly as they do on any other provider.

Can software that only speaks SMTP send through PostFrame?

Yes. PostFrame also runs an SMTP relay that authenticates with your API key and queues the message through the normal send pipeline, so legacy tools get the same templates, tracking and suppression checks as the API.

What happens when this provider returns an error?

The send moves to your next provider by priority on the same request, up to three attempts. After five failures inside five minutes the provider's circuit opens and it is skipped for sixty seconds before being tried again.

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