Check the SPF and DKIM records for the domain , thse two DNS records ensure that their emails are being sent securely and that their domain is protected from fraudulent activities.
An SPF (Sender Policy Framework) record is a type of DNS record that specifies which IP addresses are authorized to send email messages on behalf of a particular domain. In other words, it is a list of servers that are allowed to send emails that claim to be from a specific domain.
DKIM (DomainKeys Identified Mail) is a type of email authentication protocol that helps to verify the authenticity of an email message and its contents. It uses digital signatures to confirm that the message was indeed sent by the claimed sender, and that the contents of the message have not been altered in transit.