CNAME and MX

[Jeremy Lunn]

Hi,

I am fairly new to DNS.  I know the basics, but there are a few things I
am not sure about.

First of all, why are you supposed to have only one A record for each IP
address?  Is that actually stated by the RFC?

And say I make a CNAME mail.mydomain pointing to serv100.mydomain can I
use mail.mydomain as the MX or do I have to use the A record
serv100.mydomain?

Thanks,

-- 
Jeremy Lunn
Melbourne, Australia
ICQ: 19255837