Mailtrap

Send and test email through Mailtrap. Agents deliver transactional emails from verified sending domains, route test sends to sandbox inboxes, and inspect captured messages down to their rendered HTML and plain-text bodies.

10 actions API key available

Mailtrap website ↗ Platform Documentation ↗ Capability data verified 2026-07-27

A revised order-confirmation template is ready for release

Send Email to Sandbox pushes the template with representative variable sets into the QA inbox

Get Message HTML and Get Message Text pull the rendered output for each captured test send

The agent verifies subject, sender, merge variables, links, and that both HTML and text parts rendered

The rendered results post to the release channel with the diff against the previous version

The owner reviews the actual rendered email and approves promotion to production sending

Send Email delivers through the verified sending domain, and the template version is recorded as released

What This Integration Enables

Mailtrap draws the line every email operation needs: a production API that delivers from verified sending domains, and a sandbox that captures everything for inspection with zero risk of reaching a real recipient. FlowRunner agents work both sides of that line and, more importantly, respect it. On the sandbox side they send test renders, list and search captured messages, and pull exact HTML and text bodies as strings an agent can assert against. On the production side they deliver transactional email, plain text, HTML, or a stored template with variables. The workflow discipline is the point: nothing crosses from sandbox to production without a check passing and, for template changes, a person approving. - Deliver transactional email from verified domains, direct content or template UUID with variables - Rehearse templates and campaigns in sandbox inboxes where no message can escape - Assert on rendered output programmatically: subject, sender, recipients, HTML body, text body - Automate QA housekeeping with read-status updates and gated message and inbox cleanup

Without FlowRunner

Testing in production, quietly The "test" of a new template is sending it to yourself and squinting at your phone

The variable that shipped as a variable A customer receives "Hi {{first_name}}" because nobody rendered the edge case with an empty field

QA inboxes as landfill The sandbox fills with months of captured sends, and finding last Tuesday's test means scrolling

With FlowRunner

Every send rehearsed in sandbox first Templates render against real variable sets in a captured inbox where nothing escapes to a customer

Rendering verified as data Agents assert on the actual HTML and text bodies, so an unrendered variable fails a check instead of reaching an inbox

Inboxes cleaned on purpose Message deletion and inbox cleanup run as deliberate, gated steps after results are recorded, not as someone's chore

Use Case Scenarios

The order confirmation that renders before it ships

A [Shopify](/integrations/shopify) store updates its order-confirmation template. The release workflow fires Send Email to Sandbox with five variable sets, a normal order, a long product name, an empty optional field, a non-Latin name, a refund case. The agent pulls each render with Get Message HTML, checks that every variable resolved and every link carries the right domain, and posts the renders for review. Only after approval does the production flow start using Send Email for real orders.

Template QA as a regression suite

Every night, an agent replays the full template catalog into a dedicated sandbox inbox and compares rendered output against the recorded baselines, logging results to [Google Sheets](/integrations/google-sheets). When a shared partial changes and silently breaks the footer in three templates, the diff posts to [Slack](/integrations/slack) the next morning naming exactly which templates moved. Email regressions get caught the way code regressions do, before a customer sees one.

Operational sends with an audit trail

Fulfillment exceptions need customer notification. The workflow drafts the message, and for the standard cases sends immediately through Send Email, logging the returned message IDs against the order. For the sensitive cases, a refund above threshold, a recall notice, the draft renders to sandbox first and a support lead approves the exact email before the production send. The message IDs Mailtrap returns become the proof of what was sent, to whom, when.

Human-in-Loop Highlight

Send Email is the boundary crossing in this connector: everything else on this page happens inside a sandbox built so mistakes cost nothing, and this one call delivers from your verified sending domain to real recipients who cannot unreceive it. The failure modes are all expensive in trust, a broken template reaching the whole recipient list, a test that someone pointed at production, a sensitive notice sent with the wrong tone, and your domain's sending reputation absorbs every one. Clean Inbox earns the same respect for a different reason: it permanently deletes every captured message in a sandbox inbox, and with it the rendered evidence a QA run may still need. So FlowRunner workflows route template changes and sensitive sends through sandbox render plus human approval before Send Email runs, and Clean Inbox executes only after results are recorded and a person confirms the inbox is done being evidence.

Agent processes routinely

Detects exception requiring judgment

Clear match Continues automatically

Ambiguous Routes to human via preferred channel

Human decides

Agent resumes with decision

Agent Capabilities

10 actions

Production Sending

Send Email Sends a transactional email through Mailtrap's production Email Sending API from a verified sending domain. Supply text and/or HTML, or a Template UUID with variables; recipients accept comma or newline separated lists. Returns the assigned message IDs, the audit trail of what was sent.

Sandbox Sending

Send Email to Sandbox Sends a test email to a sandbox inbox instead of real recipients. The message is captured for inspection and nothing is delivered externally, which makes this the rehearsal step for every template change.

Inbox and Message Inspection

List Inboxes Lists all sandbox inboxes with ID, name, project association, and message counts. The discovery step that scopes QA workflows to the right inbox.
List Messages Lists captured messages in a sandbox inbox, most recent first, with subject, sender, recipients, and read status, optionally filtered by a search term.
Get Message Retrieves a captured message's full metadata: subject, sender, recipients, read status, size, timestamps, and links to its HTML, text, and raw bodies.
Get Message HTML Returns the rendered HTML body of a captured message as a string, the artifact QA assertions run against. Empty if the message has no HTML part.
Get Message Text Returns the plain-text body of a captured message as a string, used to verify the text part that plain-text clients and previews will show.

Housekeeping

Mark Message Read Updates a captured message's read status in either direction. Used to mark test messages processed as a QA run progresses.
Delete Message Permanently deletes a single captured message from a sandbox inbox. Cannot be undone; runs after the message's results are recorded.
Clean Inbox Deletes all captured messages from a sandbox inbox at once. Cannot be undone, which is why this page's gate requires a person to confirm the inbox has finished being evidence.

Frequently Asked Questions

What can FlowRunner do with Mailtrap?

FlowRunner agents can run Send Email, Send Email to Sandbox, and List Inboxes in Mailtrap, plus 7 more actions.

Does connecting Mailtrap to FlowRunner require OAuth?

No. Mailtrap connects to FlowRunner with an API key, no OAuth flow required.

Can Mailtrap trigger a FlowRunner workflow automatically?

Mailtrap doesn't currently expose triggers in FlowRunner. It connects as an action step inside workflows started by another trigger.

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