If an email address you control is signed-up to an email list, you are a member of that list. You can be a member of any number of lists. You may also be a member of different lists under different email addresses (if you have multiple email addresses).
You can search for your email address(es) on all the listserv.nebraska.edu lists if you are unsure of which lists you are a member.
As a member of an email list you can alter you subscription settings at Subscriber's Corner. You will have to login to see and control your subscription settings. If you haven't yet registered your email address for the listserv.nebraska.edu web interface, you might want to read the sign-up instructions.