This is very odd. I noticed that when I send using php mail() even if I set a reply-to and from header, the server sends from apache@myhostname.com. But yet if I send to a valid address and get the email it looks like it comes from right host. when I send to an invalid host, that's where it messes up, since the bounce back goes to apache@myhostname.com instead of what I specified in the from and reply-to. What would cause this?