How to force users, to use their own domain in sender's address inexim?

Hi all,
I have an exim running, that serves several domains, that belong to
different users.
I did that with this part in exim4.conf.template

vdom_aliases:
debug_print = "R: vdom_aliases for $local_part@$domain"
driver = redirect
allow_defer
allow_fail
domains = dsearch;/etc/exim4/virtual
data =
${expand:${lookup{$local_part}lsearch*@{/etc/exim4/virtual/$domain}}}
retry_use_local_part
pipe_transport = address_pipe
file_transport = address_file
# not no_more - we try again without the suffix

In the current configuration every Authenticated user (using TLS) is
allowed to send a mail with a free chosen sender's address.
How can I make sure, that every authenticated user only uses his domain
in sender's address?

Greetings
Rene