SMTP
Send email through MailBlastr over SMTP using your API key as the password.
If your application or platform already speaks SMTP, you can send through MailBlastr without touching the HTTP API. Point your SMTP client at the MailBlastr relay and authenticate with your API key. Emails sent over SMTP appear in your dashboard and event log just like API sends.
Prerequisites
- A MailBlastr API key.
- A verified domain to send from.
SMTP credentials
Configure your SMTP integration with the following credentials:
Hoststringoptionalsmtp.mailblastr.com
Portnumberoptional25, 465, 587, 2465, or 2587.
Usernamestringoptionalmailblastr
PasswordstringoptionalYour API key, e.g. mb_xxxxxxxxx.
Ports and security
The port you choose determines how the connection is secured:
| Type | Port | Security |
|---|---|---|
| SMTPS | 465, 2465 | Implicit SSL/TLS — connects directly over SSL/TLS. |
| STARTTLS | 25, 587, 2587 | Explicit SSL/TLS — connects in plaintext, then upgrades to TLS. |
587 (STARTTLS) or 465 (SMTPS) are the safe defaults; plain port 25 should only be used when it negotiates STARTTLS.Idempotency key
To prevent duplicate emails on retry, add a Mailblastr-Idempotency-Key header to the message. MailBlastr processes a given key once and ignores repeats for 24 hours — see Idempotency keys.
From: Acme <onboarding@yourdomain.com>
To: delivered@example.com
Subject: hello world
Mailblastr-Idempotency-Key: welcome-user/123456789
<p>it works!</p>Custom headers
If your SMTP client supports it, you can add custom MIME headers to your messages. Common uses:
- Add a correlation ID with a header like
X-Entity-Ref-IDfor downstream filtering. - For transactional mail, add your own
List-Unsubscribeheader. See Custom headers and Unsubscribe links.
FAQ
Where do I see emails sent over SMTP? They show up in your emails dashboard and carry the same status and event log as API sends.
Does the rate limit apply to SMTP? Yes — SMTP sends count against the same account rate limit as the HTTP API.