Imap connections are made via the IMAP protocol, and allow access to your system mail box, along with your files and folders in your account on the server.
EECS has two servers to connect to, prime.cs.ohio.edu and oucsace.cs.ohio.edu. These are the connonical names of the machines - that is, these are the names that the machines think of themselves. oucsace has an alias of ace for easier typing, and both machines are reachable via the cs, ece and eecs subdomains, in both ohio.edu and ohio.edu domains. However, you should use the connonical names of prime.cs.ohio.edu and oucsace.cs.ohio.edu when accessing these machines to avoid problems with security certificates.