What Email Relay is and when to use it
Send mail over SMTP from software you already run, without changing its code. This page helps you choose between Email Relay and Email API.
Email Relay is for software you already run that knows how to send over SMTP — a website, accounting software, an internal system — and that you simply want to point at a trustworthy sending path.
How it differs from Email Business
| Email Business | Email Relay | |
|---|---|---|
| Who sends | people, via webmail or Outlook | your software |
| 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 |
Turning on Email Relay does not take away the mailboxes you already use. Mail sent to your domain still goes exactly where it went before.
Email Relay or Email API
The two services send down the same path; only the way your software connects differs.
| Email Relay | Email API | |
|---|---|---|
| Protocol | SMTP | HTTP |
| Suits | existing software with only host/port/user/password fields | code you write yourself |
| Authenticates with | a fixed username plus an SMTP key | an API key in a header |
| Code changes | usually none | yes, one HTTP call |
The quick rule:
- Your software has fields for SMTP server, port, username, password → Email Relay
- You are writing code and can make HTTP calls → Email API
The two services have separate accounts, domains, keys and quotas. Turning on both means configuring both — except the ownership record, which is shared across all four services.
The path to your first message
- Verify domain ownership — shared by all four services
- Publish the relay sending domain records
- Create an SMTP key
- Point your software at the relay
After that, read the suppression list — it explains the addresses that "never arrive no matter how often you send".
Limits worth knowing up front
- Email Relay only sends. It does not receive mail and has no mailboxes.
- The sender address must belong to a domain activated in Email Relay.
- The SMTP username is always
apikey— not an email address. This is the single most common mistake. - Your plan sets limits on messages per day, keys and message size. The numbers for your plan are shown in the console.
Error code lookup
Look up the error codes the Email API returns, tell whether the fault is in your request or on our side, and know which codes are worth retrying.
Send your first email
Four steps from a blank domain to a message received, plus a command-line check that separates wrong settings from wrong software configuration.