where to declare

[Gerard M. Mamou]

Hello
I have a zone my.domain and a subzone bogus.my.domain
I have a Name Server ns.my.domain and ns.bogus.my.doamin (which is the
same A, same machine)
Where should I declare the MX records for bogus.my.domain 
in the file of my.domain or in the file of bogus.my.domain????

my.domain SOA ...

bogus.my.domain	IN	NS	ns.bogus.my.domain
bogus.my.domain IN	MX	mail.bogus.my.domain
...
end of db for my.domain

or

my.domain SOA ...
bogus.my.domain	IN	NS	ns.bogus.my.domain
...
end of db for my.domain

bogus.my.domain SOA ...
		IN MX mail.bogus.my.domain
end of db for bogus.my.domain

Is there any differences??
How it is resolved??
Which one come first???
Which one is better???
I have also a slave for my.domain ONLY in my ISP name server
Maybe the First method is better in case ns.bogus.my.domain come down
the record will be resolved anyway because it is in my.domain file???
Any helps?
TIA
Gerard Mamou