[CentOS] Mailers and records MX

I've installed bind on centos 4.3.. This is a part of my config file:

example.com.        IN      MX  10   mail.example.com.
example.com.        IN      MX  15   mail1.example.com.
example.com.        IN      MX  20   mail2.example.com.

mail.example.com.	IN A IP
mail.example.com.	IN A IP