help on dns and mail implementation

[arvinboy <arvin burgos menusys net>]

to all,
                     hope you can help me in my situation right now. our
head office is planning to have a mail backup server for our clients.
this are my quetions:
                   1.) i already had a running DNS server which can
resolved into my internal ip eth0( 202.58.151.59).this is my public ip
which was given from my isp and eth1(191.168.1.1) for my internal
network which also be used for my web services. how could i make this
thing work. i already ask my isp but they are not allowing me to use
their nameservers as my resolver to the outside. they told me, inorder
to use their nameservers, they are requiring me to register a domain.
any other options?
                   2.) if my dns works well, my next plan is to setup a
mail server into my server? could i possibly run my mail server into my
internal network as a test, since i am having negotiation with my isp
regarding nameserver which is related to number one.
                   3.) im using bind-9.1.3-4,
bindconf-1.6.1-1,bind-utils-9.1.3-4 and caching-nameserver-7.2-1, is
this a good package, if not what version should you recommend, i'm using

redhat7.2

                   please guide to the right track...godbless and thank
you!

arvin