This is a space-separated list of userid@host.domain type email addresses belonging to people who have authority to manage LISTSERV--specifically the people who are allowed to create lists, but also who have pretty much global authority on the server to look at lists, modify list headers, and so forth.  There are some advanced options for this setting but for right now you will probably just want to insert your own email address so that you can test the server. 

Note: The POSTMASTER should NEVER be LISTSERV@ anywhere or POSTMASTER@ anywhere.  These userids are reserved and mean specific things to LISTSERV.  If you need to use a generic name for a postmaster account, it is recommended that you use something like "listmaster" or "lstmaint" instead.