Juno Online Services started as an email only service provider. While they have expanded to be an end-user ISP, they can still be used as an email only service via one of three ways.
Juno email client
You can still use the Juno email client if you have a paid Juno account. See Juno Email Clients for details on the clients.
You can use Juno's web interface at http://webmail.juno.com/.
POP3 email client
You can use any POP3 client if you have a paid Juno account. The POP3 server is pop.juno.com at port 110 and the SMTP server is smtp.juno.com at port 25. If your ISP blocks port 25, then use port 587. When specifying your user name, include @juno.com.