How DNS Seeds node maintain the list of addresses? On bitcoin peer node discovery, the client issues DNS requests to learn about the addresses of other peer nodes. My question is how does this DNS directed service provider learn about all the addresses in the first place?
Each normal node should connect to the seeder, this connection is detected by seeder service, that will test the node and add it to the list if some basic verification pass.

Exist other additional features, like for example fetch node list from main know seeder DNS into new seeders services.