In eMule, eDonkey2000 servers are used to provide an entry point into this network. A connection to a server is necessary to access the network's resources and to make your client known to the network.
Basically a server provides only an index for the files, the connected users share. Searching for downloads or for sources of a download is done over the servers.
A server list update in eMule is only need for a first contact to the network. As soon as eMule is connected to a server it offers intelligent features like Client to Client Source exchange to find sources or automated updates to the known servers.