multiple MX records versus DNS round robin

[Bill Myers]

> That is just too simple.
> @    IN    MX    10    Mail1.domain.com.
> @    IN    MX    20    Mail2.domain.com.
> @    IN    MX    30    Mail3.domain.com
> 
> You put your first preference with the lowest "cost" 
> and if that one's down, it will go the next higher 
> cost server designated in the mail records.

But MX 10,20,30 does not load balance.  Erwin 
is asking for a recommendation for either:

@    IN    MX    10    Mail1.domain.com.
@    IN    MX    10    Mail2.domain.com.
@    IN    MX    10    Mail3.domain.com.

- or -

@    IN    MX    10    mail.domain.com.
mail.domain.com.  IN  A  i.p.addr.1
                  IN  A  i.p.addr.2
                  IN  A  i.p.addr.3

How about both? Take a look at "dig aol.com mx", which
uses multiple MX records with equal weights AND multiple 
A recs.  My local server does not round robin the MX 
records, but the AOL server does.  A question then is: 
how does sendmail or exchange handle multiple A recs 
associated with an MX.

[Not that AOL is necessarily the authority on such matters, 
but they sure have to handle alotta "You've got mail"!]

Bill Myers
Total Network Solutions
Internetwork Solutions Engineer
Email wmyers at tns-inc.com
http://www.tns-inc.com/careers.html  (Pls send resumes to me!)