If i'm using mailrelayoptions:relayforaddresses , that mean i should know all my user ip address ?
no, only your internal addresses or your users fixed ip addresses, if they have them, like ADSL or leased lines or other fixe ip always-on connections.
For your dial-up users who do not dial-up to your ip addresses, you use the SMTP AUTH technique to authenticate them, and for all your users, no matter what ip addresses they are on.
Len
