count traffic of web services

Dear Network Gurus,

I am doing several web hosting on debian with ssl, so each customer has
its own ip address.

I am asking myself if it is sufficient having an iptables incoming accept rule
on each ip on port 80 and 443 for counting all the traffic that went
throught each ip addresses.
With iptables -L -v I can count the traffic:
1706 102K ACCEPT tcp -- any any anywhere <ip-address>
tcp dpt:www state NEW,RELATED,ESTABLISHED
47 2820 ACCEPT tcp -- any any anywhere <ip-address>
tcp dpt:https state NEW,RELATED,ESTABLISHED

Do I do not need any outgoing rule? I think as long as I am connected to a webserver,
the connection on the server is at port 80 or 443 and the data flows back to me throught
the connection, I started.

What about counting traffic of qmail on <ip-address>? Incoming would be the same as above
on port 25, but what if qmail is sending mails? In this case I have to think about
outgoing traffic, right?

Thanks for help in advance!
Fabian Lienert