the ini_set (or you can set the 5th param to the mail() function) is a
return-path. If the message bounces (recipient's mailbox full, server down, whatever the reason) it gets delivered to that address. They
serve different purposes.
The dirty little secret that nobody seems to know is that the RFCs
reserve Return-path for use by the MTA servers. It can be replaced by
any of them in the routing chain and is used when mail crosses into or
out of SMTP networks. If you want a return address other than From to
stick all the way through, you have to use the Reply-to and/or Sender
headers.
Emails don't bounce to those addresses though do they? I've always thought the return-path is where an email is bounced to and reply-to etc are used by mail clients, not the mta's.
--
Postgresql & php tutorials
http://www.designmagick.com/