I check on a website a test of send, and the problem is:
“DKIM is not signed”
DomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message.
The dkim is only part of the solution. First the provider should setup the SPF records which is simpler. The dkim requires a manipulation of the message and the setup of entries in the DNS.
If the dkim can be done on the mail server (usually not available on shared) it can be setup by a system administrator.