Here are the IMAP settings for Rackspace IMAP (Exchange):
INCOMING SERVER
Account Type: IMAP
Incoming Server: secure.emailsrvr.com
Port: 993
User Name: username, like "joeblow@domain.com"
Connection Security: SSL/TLS
Authentication: Password
OUTGOING SERVER
Outgoing Server: secure.emailsrvr.com
Port: 465
User Name: username, like "joeblow@domain.com"
Connection Security: SSL
Authentication: Password