What Email API is and when to use it
Send transactional mail with one HTTP call. This page helps you choose between Email API and Email Relay, and points you to the full parameter reference.
Email API is for your application sending mail, not for a person typing it. Order confirmations, one-time codes, password resets — mail that comes out of your code.
How it differs from Email Business
| Email Business | Email API | |
|---|---|---|
| Who sends | people, via webmail or Outlook | your code |
| Has an inbox | yes | no — sending only |
| Touches your root MX | yes | no |
| Incoming mail for the domain | goes to CloudFly | unchanged, stays where it is |
That last row surprises most people: turning on Email API does not take away the mailboxes you already use. You can keep company mail with another provider and still send transactional mail through CloudFly.
Email API or Email Relay
The two services send down the same path; only the way your application connects differs.
| Email API | Email Relay | |
|---|---|---|
| Protocol | HTTP | SMTP |
| Suits | code you write yourself, new services | existing software that only speaks SMTP |
| Authenticates with | an API key in a header | an SMTP username and password |
| Code changes | yes, one HTTP call | usually none, just configuration |
The quick rule:
- Writing new code, or already able to make HTTP calls → Email API
- You have WordPress, an ERP, or accounting software with only host/port/user/password fields → Email Relay
The two services have separate accounts, domains, keys and quotas. Turning on both means configuring both — a domain verified for one does not carry over, except the ownership record, which is shared.
The path to your first message
- Verify domain ownership — shared by all four services
- Publish the sending domain records — signing and a feedback path
- Create an API key
- Send your first message
Two more are worth doing early, though neither is required to send: receive events by webhook and read the suppression list.
Where the full reference lives
The API reference is inside the console
The console has Email API → Guide. That is where the complete parameter list, HTTP error table, plan limits, webhook events and code samples live — always matching the account you are logged into, including the plan-specific numbers.
This documentation deliberately does not copy that reference. Two places listing parameters will drift apart sooner or later, and the reader has no way to tell which one is right.
The boundary between the two:
| What you need | Read it in |
|---|---|
| Parameters, code samples, the limits on your own plan | Guide in the console |
| Looking up an error code you just received | Email API error code reference |
| First-time setup, choosing a key type, troubleshooting | this documentation |
Limits worth knowing up front
- Email API only sends. To receive mail on that domain, use another service for the inbound side.
- The
fromaddress must belong to a domain activated in Email API. No exceptions. - Your plan sets limits on messages per day and per 30-day cycle, sending domains, keys and email templates. The exact numbers for your plan are shown on the Overview screen.
Trace a missing mail
Use the Email tracking screen to find where a message stopped, read the Processing outcome column, and open the detail page when you need more.
Send your first email
One HTTP call from nothing to a message received, how to read the response code correctly, and the three mistakes new accounts hit first.