Whoever currently host your DNS must have a MX record pointing toward your email host. If you can't leave your current host and must have third
party email hosting I reccommend
www.dnsmadeeasy.com. You can also
manage your dns there. They are great. But to move your email to a new
email host you will have to edit your dns MX record. If your current host
will not edit this for you, you can use Dnsmadeeasy as your dns. Then you
can just edit your registrar to use Dnsmadeeasy and control everything
yourself.