Soft Bounce from transational emails from BREVO (Sendinblue)

Soft Bounce from transational emails from BREVO (Sendinblue)

I manage the website of a client who uses your EMAIL service for the domain floranativadobrasil.com.
 And I use the BREVO email service, previously called SendinBlue, to send transactional emails about events specific to the website.

All emails sent to any email account managed by Zoho for this customer domain receive a SOFT BOUNCE.
The sender of these emails is the fictitious address site@floranativadobrasil.com.br.  Could this be the reason why Soft Bounce occurs in all recipients with emails from the organization?

O erro reportando nos LOGS da brevo é esse:

Soft bounce 15-09-2023 15:07:34
554 5.2.3 MailPolicy violation Error delivering to mailboxes