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Already tracking product usage with PostHog? Good news: you don’t need to instrument anything twice. PostHog’s realtime destinations can forward your events straight to Retain, so churn signals start flowing in minutes.
Retain identifies people by email. Make sure your PostHog setup stores an email property on person profiles (most posthog.identify() calls already do this). Events from anonymous visitors are skipped.

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How it works

PostHog sends each event to Retain as it happens. Retain then:
  • Turns $identify and $set events into customer profiles (email, name, and other traits)
  • Records your custom events (e.g. report exported) as Retain events, auto-creating them on first sight
  • Maps group analytics ($groupidentify, $groups) to Retain accounts, so B2B usage rolls up correctly
  • Ignores PostHog-internal events like $pageview, $autocapture, and $feature_flag_called
  • Deduplicates retries, so a redelivered event never counts twice
Event names are normalized to snake_case: Report Exported becomes report_exported.

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Set it up

1

Copy your Retain write key

In Retain, go to Settings → Project token and copy your write key (it starts with rk-).
2

Create the destination in PostHog

In PostHog, open Data → Destinations → New destination, search for Retain and select it.
3

Paste your write key

Paste the write key into the Retain write key field. That’s the whole configuration.
4

Filter to the events that matter

In the destination’s Filters, select your key product events plus $identify. Two reasons: Retain’s churn detection works best on high-signal events, and PostHog bills realtime destinations per trigger event (the first 10k per month are free), so filtering keeps you in the free tier.
5

Test and enable

Use PostHog’s Start testing button to fire a test event, then enable the destination. Events show up in Retain under Events, and identified users under Customers.

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Configure your events

Once events arrive, set their Importance and Expected frequency on the Events page so Retain knows what healthy usage looks like. See Track events for what each setting does.

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Troubleshooting

  • Events aren’t showing up. Check the destination’s logs in PostHog. A 401 means the write key is wrong — copy it again from Settings → Project token in Retain.
  • Events arrive but no customer is created. The person has no valid email in their PostHog person properties. Retain skips events it can’t tie to an email.
  • An event appears with a different name. That’s the snake_case normalization. Signed Up in PostHog is signed_up in Retain.
  • $pageview never arrives. By design — PostHog-internal $ events are ignored. Track a meaningful custom event instead.