feat(workflows): edit a transactional template's sender from the editor by mayteio · Pull Request #121079 · PostHog/posthog

mayteio · 2026-10-21T11:53:36Z

Problem

A transactional email can't choose who it comes from, and the editor has nowhere to set a sender name, address or reply-to.
Moving PostHog's own emails off Customer.io needs this. A security email should come from a security address and take replies there.

This is the editor half. The API that stores and checks the sender is #121871, the base of this stack.

Changes

The transactional template editor shows the sender as one line, "From Name ", with "Replies go to …" when a reply-to is set.
"Edit sender" opens a popover with sender, display name, address and reply-to. Empty fields show the sender's own values as hints.
The address field takes only the part before the @, and the sender's verified domain is fixed after it. Switching sender moves a custom address to the new domain.
An off-domain, malformed or too-long custom address shows an error inline, on the summary line, and blocks Publish.
Right after a template becomes transactional, the editor shows the sender the server stored.
Test sends default to the template's sender and keep its custom name and address.
Applying a transactional template inside a workflow email step keeps that step's own sender and reply-to.
Library templates (not transactional) and the workflow email step look the same as before.

Demo (local stack, narrated): transactional sender demo

Before	After

Edit sender	Wrong domain

The received email (local MailDev)

How did you test this code?

Manual, on a local stack with two verified MailDev senders:

Made a template transactional from the UI. The default sender was stored and shown.
In the popover, switched sender and set a display name, address and reply-to. Publish refused an off-domain address with one message, then published after the fix.
Sent through the API with a project secret key. MailDev received From: Hedgebox Security Team <security-team@posthog.com> and Reply-To: security@posthog.com.
Rendered the editor at 1440px and 820px.

Test rationale:

emailSenderFields.test.ts tables cover the address check, including the 254-character bound, and the local-part split and join. They are pure functions, so the cases stay cheap.
emailTemplaterLogic.test.ts: applying a transactional template keeps the step's own sender and reply-to.
messageTemplateLogic.test.ts: conversion shows the stored sender, with or without an edit made meanwhile.
messageTemplateTestSendLogic.test.ts: a test send uses the template's sender, name and address.
Each of these fails without its change. The API tests are in feat(messaging): store a sender and reply-to on transactional templates #121871.

Not checked:

A real SES send. Production SES already sets reply-to, so only MailDev was exercised. MailDev needed fix(cdp): pass reply-to to the local maildev transport #121872 to show the reply-to.
Publishing within about a second of the last edit leaves a duplicate draft after publish, from the existing draft autosave. It doesn't affect sends, and this PR doesn't cause it.

Release status

This change is behind a feature flag and is not available to users

Transactional templates sit behind workflows-transactional-email-api.

Docs update

None. No existing doc covers transactional template settings.

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Agent: PostHog Desktop with Claude Code, Claude Opus 5.5 (claude-opus-5-5)

Skills: improving-drf-endpoints, writing-ui-components, writing-tests, writing-user-facing-copy, recording-demo-videos, stacking-prs, writing-pr-descriptions.
The first UI stacked From, sender name, address and reply-to as separate rows with "+" buttons. It was replaced, after review on rendered screenshots, by the one-line summary with a popover.
Related: feat(workflows): add mcp tool to make an email template transactional #120056 adds an MCP tool to make a template transactional. With feat(messaging): store a sender and reply-to on transactional templates #121871, MCP can set the sender through the email template update tool.
Split into this stack to stay under stamphog's line cap: feat(messaging): store a sender and reply-to on transactional templates #121871 (API) → this PR (editor), plus fix(cdp): pass reply-to to the local maildev transport #121872 (MailDev reply-to).
The open-PR search found no other change for transactional sender or reply-to.

Created with PostHog Desktop

🤖 Generated with Claude Code

trunk-io · 2026-10-21T11:53:40Z

😎 Stack merged successfully - details.

github-actions · 2026-10-21T11:53:51Z

🤖 CI report

⚠️

Trunk lane — backend Python lane

This PR is assigned to the backend Python lane. It runs backend Python tests and may merge in parallel with PRs in other lanes.

⚠️

Complexity (TypeScript) — 5 functions above the limit (max 61)

Cyclomatic complexity above the limit in changed typescript files (10 for production files, 15 for test files). Warn only: worth simplifying when you next touch these functions.

Function	Location	Complexity	Limit
`MessageTemplate`	`products/workflows/frontend/TemplateLibrary/MessageTemplate.tsx:58`	61	10
`NativeEmailTemplaterForm`	`frontend/src/scenes/hog-functions/email-templater/EmailTemplater.tsx:532`	15	10
`NativeEmailIntegrationChoice`	`frontend/src/scenes/hog-functions/email-templater/EmailTemplater.tsx:269`	13	10
`EmailSenderSummary`	`frontend/src/scenes/hog-functions/email-templater/EmailSenderSummary.tsx:13`	12	10
`<anonymous>`	`frontend/src/scenes/hog-functions/email-templater/emailTemplaterLogic.tsx:927`	12	10

✅ Duplication (Python) — clean

New Python code duplication introduced by this branch. Fails at 70+ tokens in app code, or 150+ tokens when both copies live in test files. Advisory while the gate proves itself: extract a shared helper instead of copying.

✅ Duplication (TypeScript) — clean

New TypeScript code duplication introduced by this branch. Fails at 70+ tokens in app code, or 150+ tokens when both copies live in test files. Advisory while the gate proves itself: extract a shared helper instead of copying.

⚠️

Comment density — 4% of added code lines are comments (17 of 463)

This section warns when comments are more than 3% of the code lines a PR adds, and alerts above 6%. Before agent-assisted PRs, the typical share was about 2%. Only full-line comments count. Docstrings, generated files, snapshots, migrations, and workflow files are left out.

Comments that restate the code, record how the change came about, or narrate the next line add noise for the next reader. Keep the comments that explain a reason the code cannot show, and remove the rest. See .agents/skills/writing-code-comments/SKILL.md for the house rules.

Files with the most added comment lines:

File	Comment lines	Added lines
`frontend/src/scenes/hog-functions/email-templater/emailSenderFields.ts`	5	57
`frontend/src/scenes/hog-functions/email-templater/emailTemplaterLogic.tsx`	3	15
`frontend/src/scenes/hog-functions/email-templater/EmailSenderForm.tsx`	2	109
`frontend/src/scenes/hog-functions/email-templater/EmailTemplater.tsx`	2	60
`products/workflows/frontend/TemplateLibrary/messageTemplateLogic.ts`	2	42
`frontend/src/scenes/hog-functions/email-templater/emailSenderFields.test.ts`	1	37
`products/workflows/frontend/TemplateLibrary/messageTemplateTestSendLogic.test.ts`	1	14
`products/workflows/frontend/TemplateLibrary/messageTemplateTestSendLogic.ts`	1	18

This check does not block merging. It updates on every push and clears when the share drops.

⚠️

Bundle size — 🔺 +554 B (+0.0%)

Uncompressed size of every built .js bundle, compared against the base branch.

Total: 75.83 MiB · 🔺 +554 B (+0.0%)

No file changed by more than 1000 B.

_{Posted automatically by build-bundle-size-report · uncompressed bytes from dist-report}

⚠️

Eager graph — 2 over budget

How much code each root ships on the eager path — downloaded and parsed before the surface is interactive. Measured from the esbuild output chunks (post-tree-shake, static imports only); lazy import() / React.lazy chunks are not counted.

Root	Eager (shipped)	Δ vs base	Budget
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🟢 src/scenes/session-recordings/playlist/SessionRecordingsPlaylist.tsx stays out of src/scenes/activity/explore/EventsScene.tsx
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🟢 src/scenes/web-analytics/LiveMetricsDashboard/LiveWebAnalyticsMetrics.tsx stays out of src/scenes/web-analytics/WebAnalyticsScene.tsx
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✅ Toolbar bundle — eager 2.28 MiB within budget

What the toolbar ships to customer pages, measured from the esbuild output (minified, post-tree-shake). The eager set is the entry plus everything statically imported from it — fetched before any feature runs; deferred chunks load lazily. The eager guardrail is 5.72 MiB. Each output file must also stay below 10 MB, where CloudFront stops compressing it. The module boundary is enforced separately by check-toolbar-graph.

Metric	Size	Δ vs base	Budget
Eager (shipped) entry + static imports	2.28 MiB · 19 files	no change	`████░░░░░░` 39.9% of 5.72 MiB
Deferred (lazy)	2.10 MiB · 40 files	no change	n/a — loads on demand
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898.5 KiB	`dist/toolbar/toolbar-app-LIRVHRPD.css`
691.0 KiB	`dist/toolbar/chunk-chunk-HVEQZXL4.js`
258.3 KiB	`dist/toolbar/chunk-chunk-YUTUHJHZ.js`
131.8 KiB	`dist/toolbar/chunk-chunk-FDH2IBXT.js`
130.4 KiB	`dist/toolbar/chunk-chunk-MGILAAF6.js`
74.8 KiB	`dist/toolbar/toolbar-app-F7Q25OJS.js`
69.0 KiB	`dist/toolbar/chunk-chunk-TSAL54PB.js`
35.6 KiB	`dist/toolbar/chunk-chunk-CWKXICRU.js`
21.7 KiB	`dist/toolbar/chunk-chunk-XK3VNHDG.js`
6.8 KiB	`dist/toolbar/chunk-chunk-DV7IWQNF.js`

_{Posted automatically by check-toolbar-size · sizes are toolbar output bytes (shipped, post-tree-shake) from the esbuild metafile}

✅ Dist folder size — 🔺 +71.9 KiB (+0.0%)

Total size of the built frontend/dist folder (all assets), compared against the base branch.

Total: 1016.12 MiB · 🔺 +71.9 KiB (+0.0%)

ℹ️ MCP UI apps size — 34 app(s), 27827.8 KB JS

Built size of each MCP UI app (main.js + styles.css).

App	JS	CSS
debug	840.0 KB	208.3 KB
action	764.0 KB	208.3 KB
action-list	831.0 KB	208.3 KB
cohort	763.0 KB	208.3 KB
cohort-list	829.9 KB	208.3 KB
email-template	762.9 KB	208.3 KB
error-details	767.9 KB	208.3 KB
error-issue	764.4 KB	208.3 KB
error-issue-list	831.6 KB	208.3 KB
experiment	828.1 KB	208.3 KB
experiment-list	831.7 KB	208.3 KB
experiment-results	830.6 KB	208.3 KB
feature-flag	830.3 KB	208.3 KB
feature-flag-list	834.1 KB	208.3 KB
feature-flag-testing	766.3 KB	208.3 KB
inline-scan	763.5 KB	208.3 KB
insight-actors	829.4 KB	208.3 KB
llm-costs	826.7 KB	208.3 KB
session-recording	765.3 KB	208.3 KB
survey	764.6 KB	208.3 KB
survey-global-stats	826.8 KB	208.3 KB
survey-list	831.6 KB	208.3 KB
survey-stats	826.8 KB	208.3 KB
trace-span	763.4 KB	208.3 KB
trace-span-list	830.9 KB	208.3 KB
vision-observation-list	830.0 KB	208.3 KB
workflow	763.4 KB	208.3 KB
workflow-list	830.3 KB	208.3 KB
workflow-setup-status	763.0 KB	208.3 KB
query-results	1081.8 KB	208.3 KB
render-ui	1156.7 KB	208.3 KB
visual-review-snapshots	767.9 KB	208.3 KB
workflow-data-suggestions	765.7 KB	208.3 KB
workflow-sending-rules	764.4 KB	208.3 KB

ℹ️ MCP agent API — agent-facing tool changes

What this PR changes for agents, from the tool schema snapshots and tool definitions.

Tools changed (2):

Tool	Params	Scopes	Annotations	Schema chars
`workflows-create-email-template`				3,354 -> 4,347
`workflows-update-email-template`				3,440 -> 4,433

✅ Playwright — all passed

All tests passed.

View test results →

trunk-io · 2026-10-21T12:08:45Z

Failed Test	Failure Summary	Logs
`Scenes-App/Experiments ExperimentWithHealthFindings play-test`	The Storybook test could not find the text “Why?” because the experiment page remained stuck loading.	Logs ↗︎
`Scenes-App/Project Homepage ProjectHomepage smoke-test`	The test timed out while waiting for loading indicators to disappear.	Logs ↗︎
`Scenes-App/People/Person PersonNotFound smoke-test`	The test timed out while waiting for loading indicators or spinners to disappear.	Logs ↗︎

_{View Full Report ↗︎ ⋅ Docs}

mayteio · 2026-10-21T12:21:54Z

@PostHog review

posthog · 2026-10-21T12:21:59Z

@mayteio PostHog Review is reviewing this pull request.

posthog

PostHog Review · Standard · reviewed 7265a6b: 1 Must fix, 3 Should fix.

posthog · 2026-10-21T12:24:40Z

+        fields["from"] = EmailTemplateSenderSerializer(
+            required=False,
+            help_text="The sender a transactional template sends from. A template made transactional without "
+            "one gets the sender it was made transactional with.",
+        )


P1 · Preserve creation of templates with an empty sender

Creating a blank library template sends NEW_TEMPLATE.content.email.from === '' through saveTemplate unchanged. The new nested serializer rejects this with “Expected a dictionary, but got str”, so ordinary template creation now returns 400 even with transactional emails disabled. Normalize the empty sender away or update all existing authoring paths.

Fixed in dde6371. The email serializer treats an empty or null from as no sender, so a blank template from the editor creates again. I reproduced the 400 in the UI first. The workflow sync also ignores a legacy non-object value. test_create_email_template_with_subject_succeeds now sends the editor's from: '' shape.

posthog · 2026-10-21T12:24:40Z

+    def validate(self, data: dict[str, Any]) -> dict[str, Any]:
+        if not Integration.objects.filter(
+            team_id=self.context["team_id"], kind="email", id=data["integrationId"]


P2 · Validate missing integration IDs safely on PATCH

A PATCH containing content.email.from: {} or a sender with only name raises KeyError('integrationId') here. DRF propagates partial=True into nested serializers, so the required integer field does not reject its omission before validate runs. The endpoint returns 500 instead of a validation error; explicitly reject a missing integration ID.

Fixed in dde6371. The sender serializer now checks for a missing integrationId itself and returns a 400, "Choose an email sender." A new sender_without_an_id case is in test_rejects_an_update_that_would_stop_a_transactional_template_sending.

posthog · 2026-10-21T12:24:41Z

+            sender_id = resolve_transactional_email_sender(team_id, from_integration_id or sender.get("integrationId"))
+            template.content = {**template.content, "email": {**email, "from": {**sender, "integrationId": sender_id}}}


P2 · Merge the resolved sender into the editor after conversion

Converting a template now changes its content, but the frontend makeTransactional listener merges only transactional_hog_flow_id and updated_at from the response. The editor therefore shows “Choose sender” despite the configured sender, and editing its name produces a sender without an integration ID. Merge the returned sender into form state during conversion.

Fixed in dde6371. The makeTransactional listener merges the returned sender into both the baseline and the form, with or without an edit made during conversion. The conversion test is now a test.each over both paths.

posthog · 2026-10-21T12:24:41Z

+                        from={from}
+                        replyTo={emailTemplate.replyTo}
+                        senders={senders}
+                        onChangeFrom={(next) => setEmailTemplateValue('from', next)}


P2 · Carry custom sender overrides into test emails

After setting a custom name or address here, clicking “Send test” sends neither override. messageTemplateTestSendLogic.sendTestEmail spreads the template content, then replaces from with only the test integration ID, so the received message uses the integration's default identity. Preserve the template's name and address when constructing the test sender.

Fixed in dde6371. A test send defaults to the template's own sender and keeps its custom name and address. The send test now sets a non-default sender with overrides and asserts all three reach the email step.

posthog

PostHog Review · Standard · reviewed dde6371: 1 Must fix, 3 Should fix.

This Standard review started from the posthog-review label. Comment @posthog review --deep for a Deep review, or @posthog help to see all commands.

posthog · 2026-10-22T07:10:26Z

+        fields["from"] = EmailTemplateSenderSerializer(
+            required=False,


P1 · Normalize legacy senders when serializing stored templates

For a stored legacy content.email.from: "", list/retrieve raises AttributeError when EmailTemplateSenderSerializer reads its required integrationId. to_internal_value only normalizes incoming writes, so one existing row breaks the library listing even with transactional emails disabled. Normalize legacy senders during representation or migrate them.

Fixed in #121871 (23588b8), which now holds the API half of this stack. Reads now drop a stored from that is a string, empty, or has no integration ID, so a legacy row can't break the list or detail view. test_retrieve_message_template lists and reads each legacy shape.

posthog · 2026-10-22T07:10:26Z

+    def to_internal_value(self, data: Any) -> Any:
+        # New templates and templates saved before senders existed hold an empty string, which means no sender.
+        if isinstance(data, dict) and data.get("from") in ("", None):
+            data = {key: value for key, value in data.items() if key != "from"}
+        return super().to_internal_value(data)


P2 · Preserve saving templates from destination email editors

When a Mailgun destination uses “Save as new template”, saveAsTemplate forwards its nonempty string from unchanged. This normalization handles only "" and None, so the new nested serializer returns 400 and breaks the existing template-saving flow. Strip destination sender strings when constructing library content, or accept them here.

Fixed in #121871. A write treats any string from as no sender, so a destination's "Save as new template" saves again. test_create_email_template_with_subject_succeeds now covers the editor's blank value and a destination sender string.

posthog · 2026-10-22T07:10:26Z



+# Matches the send path, which ignores a custom address that fails these checks and sends from the sender's own.
+SENDER_ADDRESS_PATTERN = re.compile(r'^[^\s@"<>,;]+@[^\s@"<>,;]+\.[^\s@"<>,;]+$')


P2 · Bound sender addresses before running the regex

Publishing from.email containing a@, thousands of dots, and a trailing @ triggers quadratic backtracking in SENDER_ADDRESS_PATTERN. The new CharField has no length limit: 16,000 dots take about 0.7 seconds locally, and larger inputs occupy a request worker for much longer. Bound the address length before matching or use linear-time validation.

Fixed in #121871. The address field is capped at 254 characters, and the check returns before the regex for anything longer, in the API and the editor alike. A new custom_address_too_long case covers it.

posthog · 2026-10-22T07:10:27Z

+            sender_id = resolve_transactional_email_sender(team_id, from_integration_id or sender.get("integrationId"))
+            template.content = {**template.content, "email": {**email, "from": {**sender, "integrationId": sender_id}}}
            hog_flow_id = create_transactional_email_workflow(
-                team_id=team_id, user_id=user_id, content=_content(template, from_integration_id)
+                team_id=team_id, user_id=user_id, content=_content(template)


P2 · Validate the custom address against the resolved conversion sender

When a template has a custom address on sender A's domain, calling make_transactional with sender B's from_integration_id retains A's address while replacing its integration. Conversion bypasses sender_address_error, so it succeeds and sends silently use B's default address. Validate the resulting sender/address pair before creating the workflow.

Fixed in #121871. Conversion now checks the custom address against the sender it resolved and rejects it with template_not_sendable when the domains differ. A new case is in test_rejects_making_a_template_transactional_it_cannot_send.

- The transactional template editor shows the sender as one summary line, with an Edit sender popover for sender, display name, address and reply-to. - The address field takes the part before the @, and the sender's verified domain is fixed after it. - An invalid address shows inline and blocks Publish. - Making a template transactional shows the stored sender, and test sends keep the template's sender, name and address. - Applying a transactional template inside a workflow email step keeps the step's own sender and reply-to. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Generated-By: PostHog Desktop Task-Id: 90d9a51d-beba-47ba-8f50-b351327676f9

parameterai · 2026-10-22T08:20:32Z

Risk: No findings

This PR adds the frontend editor for a transactional email template's sender (from-name, address, reply-to) — a sender summary line with an edit popover, client-side address validation mirroring the server's checks, sender carry-over on template apply, and sender defaults for test sends. It is frontend-only; the storing and validating API is the stacked base PR already in pr-base. The main risk considered was a client/server validation differential, but the frontend regex, length bound, templating escape, and domain derivation exactly mirror the server's sender_address_error, and the server re-validates on save and send, so the client checks are UX only.

_{Sentinel reviewed 877fa19 · Review settings}

stamphog

Approved.

Risky sender configuration changes have owning-team and STRONG-familiarity assurance, with targeted regression tests. The current code addresses the substantive review concerns, including the remaining unmarked thread; neither historical reviews nor the bot's scanning announcement constitute a current-head review.

Author wrote 83% of the modified lines and has 4 merged PRs in these paths (familiarity STRONG).

Gate mechanics and policy version

Gate		Result
prerequisites	✓	all clear
deny-list	✓	no deny categories matched
size	✓	468L, 8F substantive, 576L/12F incl. docs/generated/snapshots — within ceiling
tier	✓	T1-agent / T1d-complex (576L, 12F, two-areas, feat)
stamphog 2.6.0		`.stamphog/policy.yml` @ `877fa19` · reviewed head `877fa19`

mayteio · 2026-10-22T09:21:52Z

/trunk merge

deployment-status-posthog · 2026-10-22T10:06:57Z

Deploy status

Environment	Status	Deployed At	Workflow
dev	✅ Deployed	2026-10-22 10:06 UTC	Run
prod-us	✅ Deployed	2026-10-22 10:20 UTC	Run
prod-eu	✅ Deployed	2026-10-22 10:22 UTC	Run

mayteio added the cross-lane-change Allow for cross lane (i.e. django + rust) changes to merge at once label Oct 21, 2026

mayteio self-assigned this Oct 21, 2026

posthog Bot reviewed Oct 21, 2026

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posthog Bot removed the reviewhog label Oct 22, 2026

mayteio force-pushed the posthog/transactional-email-sender-reply-to branch from dde6371 to 05fd57c Compare October 22, 2026 07:36

mayteio removed the cross-lane-change Allow for cross lane (i.e. django + rust) changes to merge at once label Oct 22, 2026

mayteio changed the base branch from master to posthog/transactional-email-sender-api October 22, 2026 07:36

This was referenced Oct 22, 2026

feat(messaging): store a sender and reply-to on transactional templates #121871

Merged

fix(cdp): pass reply-to to the local maildev transport #121872

Merged

mayteio added this pull request to stack #121873 October 22, 2026 07:37

mayteio changed the title ~~feat(messaging): let transactional templates set their own sender and reply-to~~ feat(workflows): edit a transactional template's sender from the editor Oct 22, 2026

mayteio force-pushed the posthog/transactional-email-sender-reply-to branch from 05fd57c to 877fa19 Compare October 22, 2026 08:01

mayteio marked this pull request as ready for review October 22, 2026 08:20

mayteio added the stamphog Request AI approval (no full review) label Oct 22, 2026 — with PostHog

pr-assigner-resolver-posthog Bot requested a review from a team October 22, 2026 08:21

stamphog Bot approved these changes Oct 22, 2026

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trunk-io Bot merged commit 3f7b986 into master Oct 22, 2026
359 of 367 checks passed

trunk-io Bot deleted the posthog/transactional-email-sender-reply-to branch October 22, 2026 09:43

		sender_id = resolve_transactional_email_sender(team_id, from_integration_id or sender.get("integrationId"))
		template.content = {template.content, "email": {email, "from": {**sender, "integrationId": sender_id}}}

		fields["from"] = EmailTemplateSenderSerializer(
		required=False,



		# Matches the send path, which ignores a custom address that fails these checks and sends from the sender's own.
		SENDER_ADDRESS_PATTERN = re.compile(r'^[^\s@"<>,;]+@[^\s@"<>,;]+\.[^\s@"<>,;]+$')

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