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.
mail() returns TRUE if the mail was successfully accepted for delivery, FALSE otherwise.
The Windows implementation of mail() differs in many ways from the Unix implementation. First, it doesn't use a local binary for composing messages but only operates on direct sockets which means a MTA is needed listening on a network socket (which can either on the localhost or a remote machine). Second, the custom headers like From:, Cc:, Bcc: and Date: are not interpreted by the MTA in the first place, but are parsed by PHP. PHP < 4.3 only supported the Cc: header element (and was case-sensitive). PHP >= 4.3 supports all the mentioned header elements and is no longer case-sensitive.
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 separate headers, although some Unix mail transfer agents may work with just a single newline (\n).
The additional_parameters parameter can be used to pass an additional parameter 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 with the -f sendmail option. 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. Since PHP 4.2.3 this parameter is disabled in safe_mode and the mail() function will expose a warning message and return FALSE if you're trying to use it.
You can also use simple string building techniques to build complex email messages.
Example 4. Sending complex email.
Note: Make sure you do not have any newline characters in the to or subject, or the mail may not be sent properly.
Note: The to parameter should not be an address in the form of "Something <firstname.lastname@example.org>". The mail command may not parse this properly while talking with the MTA (Particularly under Windows).
See also imap_mail().