SendPost App

Introduction

The SendPost App for Flows enables you to connect your workflows to SendPost, a transactional email / email-infrastructure platform. SendPost is the developer-facing sending API from the SendX family: you send transactional mail over a REST API (or SMTP), and it gives you deliverability tooling on top — sending-domain authentication (DKIM / Return-Path / DMARC / tracking CNAME), suppression lists, dedicated IPs and IP pools with auto-warmup, per-sub-account statistics, message inspection and event webhooks.

What is SendPost?

SendPost is an email infrastructure platform that lets you send transactional email and manage sending domains, suppressions, sub-accounts, stats and webhooks through its API. Key features include:

• Transactional email sending (direct HTML or template-based)
• Sending-domain authentication (DKIM / Return-Path / DMARC / tracking CNAME)
• Suppression list management
• Multi-tenant sub-accounts, each with its own API key
• Per-sub-account statistics (aggregate and daily)
• Message inspection and event webhooks
• Dedicated IPs and IP pools with auto-warmup

Getting Started

Prerequisites

Before using the SendPost App, you will need:

• A SendPost account
• Your SendPost Sub-Account API Key (required for sending email and managing that sub-account's domains/suppressions)
• Your SendPost Account API Key (optional — only required for account-level endpoints: sub-accounts, statistics, message lookup, webhooks, IPs)

Available Stages

1. Send Email — POST /api/v1/subaccount/email/ Sub-Account key;

2. Send Email With Template — POST /api/v1/subaccount/email/template Sub-Account key;

3. List Domains — GET /api/v1/subaccount/domain Sub-Account key;

4. Create Domain — POST /api/v1/subaccount/domain Sub-Account key;

5. Get Domain — GET /api/v1/subaccount/domain/{domain_id} Sub-Account key;

6. Delete Domain — DELETE /api/v1/subaccount/domain/{domain_id} Sub-Account key;

7. List Suppressions — GET /api/v1/subaccount/suppression Sub-Account key;

8. Add Suppression — POST /api/v1/subaccount/suppression Sub-Account key;

9. Remove Suppression — DELETE /api/v1/subaccount/suppression Sub-Account key;

10. List Sub-Accounts — GET /api/v1/account/subaccount/ Account key;

11. Create Sub-Account — POST /api/v1/account/subaccount/ Account key;

12. Get Sub-Account — GET /api/v1/account/subaccount/{subaccount_id} Account key;

13. Get Aggregate Stats — GET /api/v1/account/subaccount/stat/{subaccount_id}/aggregate Account key;

14. List Daily Stats — GET /api/v1/account/subaccount/stat/{subaccount_id} Account key;

15. Get Message — GET /api/v1/account/message/{message_id} Account key;

16. List Webhooks — GET /api/v1/account/webhook Account key; 

17. Create Webhook — POST /api/v1/account/webhook Account key;

18. Delete Webhook — DELETE /api/v1/account/webhook/{webhook_id} Account key;

19. List IPs — GET /api/v1/account/ip/ Account key;

Why Two Keys

This is the single most important thing to get right about SendPost. The API has two independent, non-interchangeable API keys, and the URL path tells you which one applies:

Using the wrong key (or omitting the header) returns HTTP 401 Unauthorized. Each sub-account has its own key, so a multi-tenant setup normally installs the app once per sub-account with a different Sub-Account API Key, while the Account API Key stays the same across them.

Note the counter-intuitive part: the statistics for a sub-account live under /api/v1/account/subaccount/stat/{subaccount_id} and therefore need the Account key, not the sub-account key. Likewise Get Message is an account-level lookup.

API Notes

Status codes

Known quirks handled in these blueprints

• Send Email returns an ARRAY, one element per recipient, even for a single recipient. Flows cannot index into arrays, so both send endpoints loop the response with a ForEach and accumulate it with @arrayAdd into a Results array, while also lifting the single recipient's messageId into a flat MessageID output.
• Delete Suppressions is a DELETE with a JSON body. This is the one place the house rule "no Content-Type and empty payload on GET/DELETE" is deliberately broken, because SendPost requires the {"suppressions":[...]} body. Delete Domain and Delete Webhook follow the normal rule (no body, no Content-Type).
• Add Suppression keys the body by suppression type: {"manual":[{"email":"..."}]}. The type parameter is interpolated into the JSON key position rather than branching into four near-identical Call API stages.
• HTML bodies are interpolated into a JSON payload. Keep htmlBody on a single line and use single quotes for HTML attributes (<a href='https://...'>). A raw double quote or a newline inside htmlBody or subject breaks the JSON payload and SendPost answers 422.
• limit / offset / search on the list endpoints are hardcoded to limit=100&offset=0 rather than exposed as parameters, because {{var||default}} syntax is not supported in a Call API URL.

Parameter Descriptions

Response Descriptions

How to Connect

1. Create a SendPost account at https://app.sendpost.io/register.
2. In the dashboard open the sub-account you want to send from and copy its API key. Paste it into the Sub-Account API Key connection parameter.
3. Only if you want the account-level endpoints (stats, sub-accounts, webhooks, IPs, message lookup): open Account Settings → API Keys, copy the account key and paste it into Account API Key. Leave it blank otherwise.
4. Add and verify a sending domain before you send anything — see below.

How to Test

Step 1 — verify the connection. Run List Domains with no parameters. A 200 with an empty Domains array is a valid pass: it proves the Sub-Account API Key is accepted. A 401 means the key is wrong or you pasted the account key.

Step 2 — add a sending domain. Run Create Domain with name = a domain you control, e.g. mail.acme.com. Publish the returned records in your DNS:

• DkimHost → TXT → DkimValue
• ReturnPathHost → CNAME → ReturnPathValue
• TrackHost → CNAME → TrackValue (needed for click tracking)
• DmarcHost → TXT → DmarcValue

Re-run Get Domain with the returned DomainID until Verified is true. DNS propagation is usually minutes but can take hours.

Step 3 — send. Run Send Email:

• fromEmail: [email protected] (must be on the verified domain)
• fromName: Acme Support
• toEmail: your own inbox
• subject: SendPost test from Flows
• htmlBody: <p>Hello from <b>Flows</b> - <a href='https://flows.world'>click me</a></p>
• trackOpens / trackClicks: leave empty (both default to true)

Expect RecipientCount = 1 and a MessageID UUID. The mail should arrive within seconds.

Step 4 — inspect it. Paste that MessageID into Get Message (needs the Account API Key). You get the full envelope back.

Step 5 — stats. Run List Sub-Accounts to get your numeric SubAccountID, then Get Aggregate Stats with from = today minus 7 days, to = today (YYYY-MM-DD). Processed should include your test send. Note stats can lag a few minutes.

Step 6 — suppressions. Add Suppression with email = [email protected] and type left empty (defaults to manual), then List Suppressions with a from/to window covering today, then Remove Suppression for the same address.

Every endpoint carries a pink "How to test" note on its Designer canvas with concrete example values.

Use Cases

• Transactional email from any flow — password resets, receipts, shipping notices, OTP mails, alerting. Send Email is the workhorse; Send Email With Template keeps the copy in SendPost so marketing can edit it without touching the flow.
• Self-service tenant onboarding — Create Sub-Account returns that tenant's own API key, so a flow can provision an isolated sending identity per customer and store the key.
• Automated domain onboarding — Create Domain returns the four DNS records; a flow can push them straight into a DNS provider and then poll Get Domain until Verified is true.
• Suppression hygiene — pipe unsubscribes and complaints from your CRM into Add Suppression, and honour re-consent with Remove Suppression.
• Deliverability monitoring — schedule Get Aggregate Stats daily and raise an alert when the hard-bounce or spam ratio crosses a threshold; List Daily Stats gives the per-day series for a chart or digest.
• Event ingestion — Create Webhook points SendPost at a Flows webhook trigger, turning deliveries, opens, clicks, bounces and complaints into flow runs.

Troubleshooting