Allowing relaying NOT based on an IP range

[Dimitri SZAJMAN]

Hi.

My qmail server allows relaying to 212.208.85.* cause this is my network. A
client on a (lame) ISP with dynamic IP adress would like to use my SMTP
because his SMTP is bad.

I can't allow all IP of his ISP because I would relay 193.252.*.* so
thousands of IPs.
So what can I do ? Can I set qmail to relay based on the "FROM: " field ?
Can I use an authentification for using the smtp ?

Thank you for your answer !

PS : Please forgive my bad english :)