email - How to change envelope from address using PHP mail?

Question

I am using PHP with Apache on Linux, with Sendmail. I use the PHP mail function. The email is sent, but the envelope has the Apache_user@localhostname in MAIL FROM (example nobody@conniptin.internal) and some remote mail servers reject this because the domain doesn't exist (obviously). Using mail, can I force it to change the envelope MAIL FROM?

EDIT: If I add a header in the fourth field of the mail() function, that changes the From field in the headers of the body of the message, and DOES NOT change the envelope MAIL FROM.

I can force it by spawning sendmail with sendmail -t -odb -oi -frealname@realhost and piping the email contents to it. Is this a better approach?

Is there a better, simpler, more PHP appropriate way of doing this?

EDIT: The bottom line is I should have RTM. Thanks for the answers folks, the fifth parameter works and all is well.

Answer 1

mail() has a 4th and 5th parameter (optional). The 5th argument is what should be passed as options directly to sendmail. I use the following:

mail('to@blah.com','subject!','body!','From: from@blah.com','-f from@blah.com');