DNS MX records for subdomains

[Gerry George]

I have a DNS setup & working correctly (AFAIK).

I want to create separate mail domains for departments for this  mail to be 
handled separately as follows:

My.domain	MX	10	mail.my.domain
		MX	20	other.my.domain

I would have expected that mail to user at sub.my.domain would automatically 
get handled without the need for a wildcard DNS record.  However, the DNS 
server would respond with a "domain unknown" type of error.

I ended up doing
My.domain	MX	10	mail.my.domain.
		MX	20	other.my.domain.
sub1		MX	10	mail.sub1.my.domain.
		MX	20	mail.my.domain.
		MX	30	other.my.domain.
sub2		MX	10	mail.sub2.my.domain.
		MX	20	mail.my.domain.
		MX	30	other.my.domain.

This correctly gets the mail to the sub-domain mail server.  Is this the 
expected BIND behavior and were *my* expectations incorrect?

system: Linux (SuSE 6.4) & BIND 8.x

Gerry George

Gerry E. George  <ggeorge at digisolv.com>
Information Technology Specialist,
DigiSolv, Inc.
(758) 450-3444 / 3109 (fax)
http://www.digisolv.com