Write/Read Permission OWA 2003

My company has recently setup OWA service for access
from the internet. Users are able to access the
service, they can read their messages. However they
are not able to create/send new messages neither can
they delete any. We’ve checked permissions
from /exchange virtual hosts in IIS and from system
manager and in both cases the execute permission have
been enabled. Anybody there with an idea of what
needs to be done to resolve this. Regards.