SMTP Tester
Provider & MTA setup

Brevo SMTP test: SMTP key, ports, and troubleshooting

Brevo SMTP test for smtp-relay.brevo.com on port 587 with STARTTLS. Use your SMTP login and SMTP key (not the v3 API key) as credentials.

10 min read Credentials redacted No signup

Connection settings

Host
smtp-relay.brevo.com
Port
587
Security
STARTTLS

Brevo (formerly Sendinblue) provides transactional SMTP relay at smtp-relay.brevo.com on port 587 with STARTTLS. The most common mistake is using the v3 REST API key as the SMTP password: Brevo issues separate credentials for SMTP and REST. This guide covers the exact settings, the SMTP key, how to read the handshake transcript, and the most frequent errors (535 auth failures, 550 sender rejections, 421 throttling).

Recommended settings

Field Value
Host smtp-relay.brevo.com
Port 587 (STARTTLS) or 465 (implicit TLS)
Security STARTTLS on 587, TLS on 465
Username The SMTP login shown on the SMTP settings page (often your Brevo account email)
Password An SMTP key generated in the dashboard (not the v3 API key)
Auth method Auto, PLAIN, or LOGIN
From address A validated sender or an address on an authenticated domain

587 with STARTTLS is the standard choice for client submission; see SMTP port 587 vs 465 for the tradeoffs.

Finding your SMTP credentials

  1. Log in to the Brevo dashboard.
  2. Open the SMTP & API settings (under your profile / Settings menu, depending on the dashboard version).
  3. Select the SMTP tab. You will see:
    • SMTP login: the username Brevo expects. In most accounts this is your Brevo account email address, but treat the value shown on the page as authoritative. Brevo may display a generated SMTP key username instead for some accounts.
    • SMTP keys: a list of generated keys. Click the option to generate a new SMTP key if none exist.
  4. Copy the SMTP key value. This is your SMTP password.

The exact labels and menu locations shift as Brevo updates its dashboard, so trust the section named "SMTP" and its login/key fields rather than a fixed path.

Three credentials people confuse:

Credential Works for SMTP?
SMTP key (from the SMTP tab) Yes
v3 API key (from the API keys section) No, REST API only
Your Brevo account password No

Do not use the v3 API key even though it looks similar. It is a bearer token for HTTP calls to api.brevo.com and fails SMTP authentication every time. For background on the handshake stages this guide references, see what is an SMTP test.

Sender validation vs domain authentication

Brevo will not deliver mail from an address it cannot attribute to you, even with valid SMTP credentials. Two mechanisms cover this, and they are not the same thing:

For a one-off test, a validated sender is enough. For production, authenticate the domain: DKIM-signed mail with aligned SPF and DMARC survives spam filters far better than unsigned mail from a lone validated sender.

Testing with SMTP Tester

  1. Host: smtp-relay.brevo.com, port 587, security STARTTLS.
  2. Username: the SMTP login shown on the SMTP settings page.
  3. Password: the SMTP key you copied.
  4. From: a validated sender address or an address on an authenticated domain.
  5. To: your own mailbox so you can confirm delivery end to end.
  6. Click Run. A 235 Authentication succeeded response confirms login.
  7. A 250 OK after DATA means Brevo accepted the message for delivery.

Run the full test (message included), not just the handshake, when validating a new setup. The handshake proves credentials; DATA additionally proves your From address is accepted, which is where 550 errors live.

What each transcript stage means

Common errors

535 "Authentication failed" / "Unauthorized" / "Key not found"

For a deeper walkthrough of this class of failure, see fixing SMTP authentication error 535. Some clients surface this family of failures as 401 Unauthorized in their own logs; the SMTP-level code to look for in the transcript is 535.

550 "Sender address rejected" / "Not authorized"

The From address is not validated or your domain is not authenticated. Fix options:

Brevo enforces sender attribution to prevent abuse. The rejection is not a bug in your SMTP client; fix it in the dashboard and rerun the test.

421 "Too many connections" / rate limit

Brevo throttles concurrent connections and message rates by plan. On the free plan the practical cap is around 300 emails per day; paid tiers raise the ceiling along with per-hour connection limits. Exact numbers change as Brevo revises its plans; check the limits page in your account. If you see 421 responses, wait before retrying, and audit for loops (a cron job firing every minute is the usual culprit).

Connection timeout

Daily limits and plan caps

Plan tier Practical daily capacity
Free Around 300 emails per day
Starter Monthly quota, no per-day hard cap for typical volumes
Business / Enterprise Higher quotas plus throughput options

Brevo counts against your quota whether you send via SMTP or the API, and exhaustion usually shows up as 421 throttling rather than a clean quota error. If tests pass but scheduled sends fail later in the day, check the remaining quota in the dashboard first.

Nodemailer example

A minimal Node.js setup that mirrors the test above:

import nodemailer from "nodemailer";

const transporter = nodemailer.createTransport({
  host: "smtp-relay.brevo.com",
  port: 587,
  secure: false, // STARTTLS on 587
  auth: {
    user: process.env.BREVO_SMTP_LOGIN, // SMTP login from the dashboard
    pass: process.env.BREVO_SMTP_KEY,   // SMTP key, not the API key
  },
});

// validate credentials without sending
await transporter.verify();

await transporter.sendMail({
  from: "noreply@yourdomain.com", // validated sender or authenticated domain
  to: "you@example.com",
  subject: "Brevo SMTP check",
  text: "Sent via smtp-relay.brevo.com on port 587.",
});

Notes: secure: false is correct for port 587 (nodemailer upgrades to TLS via STARTTLS); set secure: true only with port 465.

WordPress and CMS plugins

WordPress SMTP plugins (WP Mail SMTP, Post SMTP, FluentSMTP) commonly fail with Brevo because users paste the API key into the password field. Always use:

Test in SMTP Tester first to confirm credentials work before debugging the plugin. If the relay test passes but WordPress still fails, check that the plugin's "from email" matches a validated sender; that mismatch produces the 550 error even with perfect credentials.

Transactional vs marketing campaigns

Brevo separates the two:

Do not route bulk newsletters through the SMTP relay: it violates provider rules and burns your transactional reputation. Keep transactional SMTP credentials for application-triggered mail only.

Brevo SMTP vs Brevo API

Both interfaces deliver through the same infrastructure:

Use SMTP when you need plug-and-play compatibility with existing systems; use the API for programmatic control. Sender and domain setup is shared, so switching later is easy.

Legacy hostname

If you see smtp-relay.sendinblue.com in older documentation or configs, it still works (DNS redirects to Brevo infrastructure), but update to smtp-relay.brevo.com for future-proofing. The credentials are the same.

Security notes

Related guides

Frequently asked questions

Is the SMTP key the same as my Brevo account password?

No. The SMTP key is a separate credential generated on the SMTP settings page and used only for SMTP authentication. Your account password logs you into the dashboard and never works as an SMTP password. Regenerating the key invalidates the old one, so update every application that uses it.

Why does my v3 API key fail as the SMTP password?

The v3 API key authenticates HTTP requests to api.brevo.com. The SMTP relay uses a different credential system. Brevo shows both under SMTP & API settings; use the one on the SMTP tab.

How many emails can I send per day on the free plan?

Around 300 emails per day, subject to change as Brevo updates its plans. Test messages and production sends both count toward the cap, so heavy testing eats a slice of your quota. Check the limits shown in your account for the current number.

Can I send marketing campaigns over the SMTP relay?

Technically the relay accepts message data, but no. Campaigns belong in Brevo's campaign tools, which handle consent, unsubscribes, and per-campaign limits. Sending bulk marketing through transactional SMTP risks your deliverability and account standing.

Do I need both a validated sender and an authenticated domain?

At least one is required. A validated sender covers a single confirmed address and is fine for testing. An authenticated domain (DKIM, SPF, optionally DMARC) covers every address on it and improves deliverability, so use it for anything production-facing.

Does the old Sendinblue hostname still work?

Yes, smtp-relay.sendinblue.com currently resolves to the same infrastructure and accepts the same credentials. Update your configuration to smtp-relay.brevo.com anyway, since the legacy hostname is not guaranteed to keep working.

Try it on your own server

Run these settings against your SMTP server and watch the live, credential-redacted protocol transcript.

Open SMTP Tester →

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