Brevo SMTP 535 authentication failed checklist
A focused checklist for fixing Brevo SMTP authentication failures before relying on transactional delivery.
Email checks
- Confirm the SMTP host, port 587, STARTTLS setting, and Brevo SMTP login exactly match the provider dashboard.
- Use the Brevo SMTP key or password from private environment variables, not an API key pasted into source code.
- Verify the sender address is approved and uses the same domain you authenticated with SPF, DKIM, and DMARC.
- Send one low-volume transactional test, then inspect the provider response, mailbox headers, and delivery logs.
Free helpers
Build a Brevo or SMTP launch checklist, then draft starter SPF and DMARC records for the sender domain.
Paid pack
Get the private transactional email launch pack for SMTP relay, sender DNS, delivery logs, support, and rollback notes.
Short checkout: https://buy.signal-shelf.com/brevo. No subscription. Private delivery after Stripe confirms payment.
Operational email-delivery checklist only. Confirm DNS and provider settings in your own Brevo, DNS, and mailbox dashboards.