Q:

Changing web host but not mail host

I have a client who switched their web hosting to my linode, but wants to keep their mail services on bluehost.
Everything web-related switched over fine. I'm encountering undeliverable mail when sent to their email addresses.
I added this CNAME record for their domain, vtcyt.com:
Hostname: mail, Aliases to: box495.bluehost.com, TTL: Default
Do I need to add an MX record? If so, I'm not sure what it might be. Perhaps in place of the CNAME?
The error I'm receiving looks like this:
Technical details of permanent failure: 
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 554 554 5.7.1 : Relay access denied (state 14).
Any help would be appreciated. I'm not a superbly experienced server admin, especially when it comes to mail-related issues.
Thank you very much!

A:

It does not look like the domain has a MX record defined. One should be in place pointed to the bluehost email server.

