Transport Layer Security
It is not recommended to use self-signed certificates in production environments. If you do not have a suitable certificate, you can apply to a Certificate Authority to obtain one.
DomainKeys Identified Mail (DKIM)
In order to use DomainKeys Identified Mail Authenticated Received Chain (DKIM/ARC) email authentication, you need to upload your private key to the system by creating a new entry with DomainKeys Identifier Mail (DKIM) use case under under Settings > Certificates.
For for further details see Policy
Digitally signing notification, alert and report emails
In order to use Secure/Multipurpose Internet Mail Extensions (S/MIME) to digitally sign notification, alert and report email s, you need to upload your certificate and private key to the system by creating a new entry with Secure/Multipurpose Internet Mail Extensions use case under under Settings > Certificates.
For further details see Alert, notification and quarantine report emails.