If you're looking for an email *client* that does calendaring and runs on CentOS, I believe that Mulberry will talk calendaring to an exchange server and I know it runs on CentOS (as well as other Linux variants, Mac and Windows). <http://www.mulberrymail.com/> Don't let the lack of recent updates scare you off; it's a solid product, plus there are Linux users who have been updating the source tree since this previously-commercial product went open source. In the context of email, I'm using Mulberry in an environment where I have multiple imap & smtp servers, multiple accounts, and one *account* in particular has >300 sub-mailboxes with ~600,000 messages. Mulberry is the only client that I've tried that doesn't choke. Devin