DNS reverse lookups sees old server

[Mitch]

Hello all,
I hope that this is the appropriate group, but I wasn't sure where to
start...  I've got a reverse lookup issue with our mail server.  The
problem is that I do the host command on a linux box and it sees the
IP address (eg: host mail.mycompany.com    returns    208.25.66.194)  
then I do host on the IP address    (eg: host 208.25.66.194    returns
    oldmail.mycompany.com).  The problem is that doing the host
command on our mail server IP returns the name of the old mail server
and I'm not sure where to go to fix it!...  I'm somewhat failiar with
DNS and how it works, but I didn't setup the system here and could use
some help in figuring out where to start.

Thanks!