which one create the accounts/domains folders? jamm or postfix?

hi there,
when i create a new domain in jamm,
the corresponding folder in /home/vmail/domains is not created by 
default, nor the users folders.
is it jamm's work to do that? or postfix does it automatically? when? 
which rights are needed?
all my /home/vmail directory belongs to vmail, group vmail.
for the moment, i must manually create the domain/users folders, then i 
can log in the new accounts i created.
what's wrong?
Thanks in advance,
Tristan



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