One thing it can be difficult to control with this function is the envelope "from" address. The envelope "from" address is distinct from the address that appears in the "From:" header of the email. It is what sendmail uses in its "MAIL FROM/RCPT TO" exchange with the receiving mail server. It also typically shows up in the "Return-Path:" header, but this need not be the case. The whole reason it is called an "envelope" address is that appears _outside_ of the message header and body, in the raw SMTP exchange between mail servers.

The default envelope "from" address on unix depends on what sendmail implementation you are using. But typically it will be set to the username of the running process followed by "@" and the hostname of the machine. In a typical configuration this will look something like nobody@yourserverhost.com.

If your emails are being rejected by receiving mail servers, or if you need to change what address bounce emails are sent to, you can change the envelope "from" address to solve your problems.

To change the envelope "from" address on unix, you specify an "-r" option to your sendmail binary. You can do this globally in php.ini by adding the "-r" option to the "sendmail_path" command line. You can also do it programmatically from within PHP by passing "-r address@domain.com" as the "additional_parameters" argument to the mail() function (the 5th argument). If you specify an address both places, the sendmail binary will be called with two "-r" options, which may have undefined behavior depending on your sendmail implementation.

for ex: mail("you@yourmail.com","Test Email","This is a test message",$headers,"-r you@yourmail.com")

With the Postfix MTA, later "-r" options silently override earlier options, making it possible to set a global default and still get sensible behavior when you try to override it locally.

On Windows, the the situation is a lot simpler. The envelope "from" address there is just the value of "sendmail_from" in the php.ini file. You can override it locally with ini_set().