[exim] How to check user activity ?

Hello

I would like to check user activity (all using SMTP AUTH) and be warned
every X messages sent or Y kb sent or Z errors

the idea is to put a call to a perl function into the transport passing
$authenticated_id
$message_size
acl_var

where acl_var is a var that will be set into acl_rcpt using

 warn set acl_var =
      hosts = +relay_from_hosts
      set acl_var = recipient/defer_ok/callout=10s,defer_ok,use_sender

each call to the perl funtion will mean a sent email,
the perl function will then do some test against a list of users and limits
and send warning emails if case


question, is the transport the correct location to put the function ?
also, will all the three parameters ($authenticated_id, $message_size and
acl_var) be visible at that level ?

Thanks in advance for any comment
Best Regards
Flaviano