Forwarding Mail Server

The situation is like this, Currently i have a domain which is hosted at xyzhost.com, in my domain registrar' the name servers are pointing to this hosts addresses,

Now what i need to do is, due to client's requirements, i need this domain to be hosted to their own server which has static ip's as well, but initially i need that just mail(exchange server being deployed) should be forwarded or configured in such a way that the domain is hosted at xyzhost.com, but mail is handled by a different server located elsewhere.And eventually both web server and mail server are our own.

now what i dont know is what should i modify at the domain registrar(i use domainsite) so that the web site still works fine(coz the site shouldnt be down) and the mail should work on the exchange server that the client has in the office.

would appreciate any help anyone can offer on this issue, i think its MX records to be modified but not sure and want to get you guys advice and suggestions as well.