The cleanest split
The cleanest split is not "PostHog or Sequenzy." It is usually:
- PostHog owns product truth.
- Sequenzy owns customer email.
- Events and outcomes move between them deliberately.
That split works because analytics and messaging have different maintenance burdens. Analytics needs clean events, cohorts, funnels, retention analysis, experiments, and debugging context. Messaging needs subject lines, templates, suppression rules, transactional reliability, unsubscribe behavior, deliverability, approvals, and campaign iteration.
PostHog Workflows is compelling because it collapses the gap between product data and action. Sequenzy is compelling because it keeps email from becoming an accidental side effect of product analytics.
When PostHog Workflows is enough
Start with PostHog Workflows when the automation is short and obvious:
- A user completes onboarding, send a quick follow-up
- A high-intent account visits pricing three times, alert Slack
- A webhook should fire after an event
- A user property needs to update after a condition
- A simple drip should run from a product event
Those workflows are close to the product. Keeping them in PostHog avoids sync delays, duplicated segments, and extra tooling.
When Sequenzy becomes the better home
Move email to Sequenzy when the work starts sounding like a lifecycle program:
- Onboarding paths differ by persona, plan, or activation state
- Trial conversion email depends on usage and billing status
- Payment failure emails need retry logic and tone control
- Transactional and marketing messages should share customer context
- Someone needs to manage drafts, templates, and reporting every week
- AI agents or scripts should help operate campaigns through API, CLI, or MCP
That is no longer just "send a message from a workflow." That is customer communication infrastructure.
The mistake to avoid
The mistake is treating the workflow builder as the owner of every customer touch just because it can send messages.
PostHog Workflows can send email. That does not automatically make it the best place to run email. Sequenzy can react to product events. That does not make it a product analytics system.
Good architecture keeps each tool close to its job.
Final recommendation
If you are early and already use PostHog, start with PostHog Workflows for simple product-triggered actions. It is fast, clean, and honest.
If email becomes important enough that people debate copy, segmentation, conversion, deliverability, and customer state every week, put it in Sequenzy. Keep PostHog as the measurement layer and make the email system responsible for the message.