qmail delivery of emails sent to user@serverFQDN ?

When a domain is added in siteworx, a real unix user account is created for it. For example, suppose I add a domain “leaderswinforever.org”, files for this site are owned by unix username “leadersw”

I noticed that qmail will accept emails sent to user@serverFQDN , where user is the unix username (ie: leadersw in the above example) and serverFQDN is the server’s FQDN (not the hosted domain.)

My questions are:

  1. where do these emails go? Are they saved somewhere or do they go to /dev/null?
  2. is there a way to configure qmail not to accept such messages?