CirrostratusOne of the better resources I have used over the year is by Zytrax, called DNS for Rocket Scientists. http://www.zytrax.com/books/dns/
In general, if you are providing authoritative DNS, you should also service reverse DNS for any IP blocks that you manage. I'd say it's not strictly required, but it is a good practice. If you have IP blocks assigned through IANA or through a carrier on your behalf, you should be able to point them to your DNS server pretty easily.
Some mail providers will reject mail originating from a host that doesn't have a reverse DNS record, or if that reverse DNS record doesn't manage a MX record for the domain.
