PHP mail: What does -f do?

Question

While troubleshooting a contact form with an e-mail host they told me to use \'-f\' in the from address of the php mail function. What does the \"-f\" flag do and why would

Answer 1

-f is a parameter to the mailer (usually sendmail). From the docs:

The additional_parameters parameter can be used to pass additional flags as command line options to the program configured to be used when sending mail, as defined by the sendmail_path configuration setting. For example, this can be used to set the envelope sender address when using sendmail with the -f sendmail option.

Here is the man page for sendmail, you can see what the -f option does:

-fname           Sets the name of the ``from'' person (i.e., the sender of the
                 mail).  -f can only be used by ``trusted'' users (normally
                 root, daemon, and network) or if the person you are trying to
                 become is the same as the person you are.