It's not enough. To receive mail, in any form, you must also have a mail server which listens for incoming mail. PHP is a server-side language that works with the web server, it can't be used for sending/receiving mail as it runs based on requests.
Even the basic mail function only runs if there's a sendmail program installed.
If you have an email server installed, you can make your script to read user's mail folder for incoming mail and displaying it (even to read it and store it in a database) and use the mail function to send mail.
