mail() automatically mails the message specified in message to the receiver specified in to. Multiple recipients can be specified by putting a comma between each address in to. Email with attachments and special types of content can be sent using this function. This is accomplished via MIME-encoding - for more information, see this Zend article or the PEAR Mime Classes.
The following RFC's may also be useful: RFC 1896, RFC 2045, RFC 2046, RFC 2047, RFC 2048, and RFC 2049.
mail() returns TRUE if the mail is successfully sent, FALSE otherwise.
If a fourth string argument is passed, this string is inserted at the end of the header. This is typically used to add extra headers. Multiple extra headers are separated with a carriage return and newline.
Note: You must use \r\n to seperate headers, although some Unix mail transfer agents may work with just a single newline (\n). The Cc: header is case sensitive and must be written as Cc: on Win32 systems. The Bcc: header is also not supported on Win32 systems.
The additional_parameters parameter can be used to pass additional parameters to the program configured to use when sending mail using the sendmail_path configuration setting. For example, this can be used to set the envelope sender address when using sendmail. You may need to add the user that your web server runs as to your sendmail configuration to prevent a 'X-Warning' header from being added to the message when you set the envelope sender using this method.
Note: This fifth parameter was added in PHP 4.0.5.
You can also use simple string building techniques to build complex email messages.
Note: Make sure you do not have any newline characters in the to or subject, or the mail may not be sent properly.