Use an Office 365 email account to send outgoing mail from Loome Publish.

You will need to create an Azure Application Registration with the Microsoft Graph application permission of Mail.Send and provide the Client Id and Tenant Id here.

Pair this with an Application Access Policy to limit what mailboxes can be sent on behalf of with this Client Id -

You will need to store the User Principal Name and Client Certificate in an Azure Key Vault.

Enable a Managed System Identity on this Azure App Service and provide it access to the Azure Key Vault using Get and List secret and certificate permissions.

Provide the names of the secrets used for the User Principal Name and Client Secret here.

Enter the Tenant Id of the Azure Ad app registration.
Enter the name of the secret that contains the User Principal Name in your Azure Key Vault.
Enter the Client Id of the Azure Ad app registration.
Enter the name of the certificate of the Azure Ad app registration in your Azure Key Vault.
Enter the URI from your Azure Key Vault.