Faking 'From' Email Address in forum sent email

[androidia]

Basically as the title says, I want to fake the 'from' field on forum sent email (e.g: new user registration).

I want to do this so any emails that get auto-sent from the board, a user/spammer wont be able to reply directly to it. Mainly to reduce inbox spam and such.

Any ideas on how I can accomplish this?

I don't care if its not changeable via the admincp, I'm just looking for a way to prevent people from replying to the auto-generated emails. I.E: registration confirmations and such. so if they it reply, it shows to: do-not-reply@url.tld rather than webmaster@url.tld. Understand what I'm getting at?

Thanks.