custom_return_path_prefix is used only when CNAME is created, despite being in postal.yml?

[JohnHammell]

postal.yml has a setting for custom_return_path_prefix in the DNS section with a default value of "psrp". This setting is not in the postal.yml by default but is listed in https://github.com/postalserver/postal/blob/main/doc/config/yaml.yml

Am I correct that this setting is only actually used by Postal when the CNAME is present in the actual DNS records and not simply when the setting (example: "custom_return_path_prefix: psrp") is present in postal.yml?

I had that setting in postal.yml & sent a test email after restarting postal. However, psrp.example.com was not present in the mail headers. However, it was only when I added in the CNAME of psrp into my actual CNAME DNS records that psrp.example.com started being used & was present in the email headers.

If this is correct, I suppose that means custom_return_path_prefix will only ever be used when it is in DNS and that return-path will solely be the setting used in return_path_domain ?