SPF, DKIM, and DMARC has been set up for the domain luan.eng.br. I recommend sending a test email to https://www.mail-tester.com/ to make sure everything is configured correctly. If you get less than a 10/10 please post the link to the full report so we can fix any other issues that there may be.
How are you sending the emails? Mail client? PHP software on the server? Roundcube webmail client? Paper and ink?