two domains and secondaries

[A.R.]

I have two questions:

1. I have one mail server called world-domination.com.  I have added two
new domains
at the nic wd.com and wd1.com.  I want to be able to use this one mail
server to serve
mail for the same set of users.  For example, harpo at world-domination.com
works great.
But, i want harpo at wd.com and harpo at wd1.com to work exactly the same.
What is
the "DNS" magic that needs to happen to allow this to work?
-Multiple cnames?
-Multiple mx's?

2. Could someone describe for me how secondary dns servers get updated
by primary
dns servers?  Specifically, if i change the records on the primary, how
long, and what
are the details of the file update/transfer on the slave (or
secondaries)?


Thanks for your help.  Please use no more than 2 syllable words in your
response.


Thanks in advance.

Warmest regards,


A. Rahman
Systems Engineer