This tutorial is to setup Thunderbird for use with CIS email accounts.
Download Link: http://www.mozilla.org/en-US/thunderbird/
If this is the first time starting Thunderbird, a 'Mail Account Setup' window will pop up. Otherwise:
File> New > Mail Account...
Enter your Name, CIS email address, and CIS password into the fields.
Ensure that IMAP w/ mail.cis.rit.edu is in the Incoming Server field.
Click Create Account.