Brevo can act as the email delivery provider for SMTP-capable stack services.
Brevo integration for the OpenSMTPD stack
Brevo fits into this stack through SMTP workflows. This page explains how it is actually used with the OpenSMTPD stack, not just that the provider exists.
How Brevo is used with this stack
The provider is useful only when it fits a concrete workflow in the stack. These are the roles it can play around the OpenSMTPD stack.
Relay outbound email through this provider
Brevo can be used by SMTP-capable services in the stack for reliable provider-backed email delivery.