I can't receive gitlab emails sent to a specific domain

Hi, I’m trying to send invitations to my co-workers join a group created on GitlLab (they doesn’t have a GitLab account), but when I send the invitations to a specific domain, for example, username@traumazero.com, it isn’t delivered. If I tried to another domain, for example, username@traumazero.com.br it is delivered ok. These doamains are both configured and receiving emails in our Office 365 account. When I contacted Microsoft support, they said that everything is ok with our Office 365 account, and they advised me to contact GitLab to check if any of their email servers are blacklisted. How do I proceed to receive these emails? I want to send invitations to username@traumazero.com because the domain @traumazero.com.br will be deprecated.