Relaying advice

[Rodrigo Borges Pereira]

Hi!

I need to provide users with the ability to send mail to anywhere. But since
that can make my server an open relay, i was thinking of a solution where a
user must receive mail before sending, thus proving that he can use the
server for relaying.

At this moment, qmail only accepts mail for domains listed on rcpthosts.

I need some advice on how can this be implemented. If there is a better
solution, also let me know.
If this is well documented somewhere, let me know.

TIA