由于标记原因，我多次将自定义标头传递给wp_mail(), 但实际上只有头的最后一个实例被发送。看来wp_mail() 正在筛选自定义标头，以便只发送唯一的标头。
我相信这是因为wp_mail 函数定义（wp includes/pluggable.php，第173行）自定义头通过添加到关联数组（第303行）进行处理：
$headers[trim( $name )] = trim( $content );
有没有一种方法可以在不修改
wp_mail 功能本身？
WP Codex for wp_mail()
wp_mail() Source code
function wp_mail( $to, $subject, $message, $headers = \'\', $attachments = array() ) {
// Compact the input, apply the filters, and extract them back out
/**
* Filters the wp_mail() arguments.
*
* @since 2.2.0
*
* @param array $args A compacted array of wp_mail() arguments, including the "to" email,
* subject, message, headers, and attachments values.
*/
$atts = apply_filters( \'wp_mail\', compact( \'to\', \'subject\', \'message\', \'headers\', \'attachments\' ) );
if ( isset( $atts[\'to\'] ) ) {
$to = $atts[\'to\'];
}
if ( !is_array( $to ) ) {
$to = explode( \',\', $to );
}
if ( isset( $atts[\'subject\'] ) ) {
$subject = $atts[\'subject\'];
}
if ( isset( $atts[\'message\'] ) ) {
$message = $atts[\'message\'];
}
if ( isset( $atts[\'headers\'] ) ) {
$headers = $atts[\'headers\'];
}
if ( isset( $atts[\'attachments\'] ) ) {
$attachments = $atts[\'attachments\'];
}
if ( ! is_array( $attachments ) ) {
$attachments = explode( "\\n", str_replace( "\\r\\n", "\\n", $attachments ) );
}
global $phpmailer;
// (Re)create it, if it\'s gone missing
if ( ! ( $phpmailer instanceof PHPMailer ) ) {
require_once ABSPATH . WPINC . \'/class-phpmailer.php\';
require_once ABSPATH . WPINC . \'/class-smtp.php\';
$phpmailer = new PHPMailer( true );
}
// Headers
$cc = $bcc = $reply_to = array();
if ( empty( $headers ) ) {
$headers = array();
} else {
if ( !is_array( $headers ) ) {
// Explode the headers out, so this function can take both
// string headers and an array of headers.
$tempheaders = explode( "\\n", str_replace( "\\r\\n", "\\n", $headers ) );
} else {
$tempheaders = $headers;
}
$headers = array();
// If it\'s actually got contents
if ( !empty( $tempheaders ) ) {
// Iterate through the raw headers
foreach ( (array) $tempheaders as $header ) {
if ( strpos($header, \':\') === false ) {
if ( false !== stripos( $header, \'boundary=\' ) ) {
$parts = preg_split(\'/boundary=/i\', trim( $header ) );
$boundary = trim( str_replace( array( "\'", \'"\' ), \'\', $parts[1] ) );
}
continue;
}
// Explode them out
list( $name, $content ) = explode( \':\', trim( $header ), 2 );
// Cleanup crew
$name = trim( $name );
$content = trim( $content );
switch ( strtolower( $name ) ) {
// Mainly for legacy -- process a From: header if it\'s there
case \'from\':
$bracket_pos = strpos( $content, \'<\' );
if ( $bracket_pos !== false ) {
// Text before the bracketed email is the "From" name.
if ( $bracket_pos > 0 ) {
$from_name = substr( $content, 0, $bracket_pos - 1 );
$from_name = str_replace( \'"\', \'\', $from_name );
$from_name = trim( $from_name );
}
$from_email = substr( $content, $bracket_pos + 1 );
$from_email = str_replace( \'>\', \'\', $from_email );
$from_email = trim( $from_email );
// Avoid setting an empty $from_email.
} elseif ( \'\' !== trim( $content ) ) {
$from_email = trim( $content );
}
break;
case \'content-type\':
if ( strpos( $content, \';\' ) !== false ) {
list( $type, $charset_content ) = explode( \';\', $content );
$content_type = trim( $type );
if ( false !== stripos( $charset_content, \'charset=\' ) ) {
$charset = trim( str_replace( array( \'charset=\', \'"\' ), \'\', $charset_content ) );
} elseif ( false !== stripos( $charset_content, \'boundary=\' ) ) {
$boundary = trim( str_replace( array( \'BOUNDARY=\', \'boundary=\', \'"\' ), \'\', $charset_content ) );
$charset = \'\';
}
// Avoid setting an empty $content_type.
} elseif ( \'\' !== trim( $content ) ) {
$content_type = trim( $content );
}
break;
case \'cc\':
$cc = array_merge( (array) $cc, explode( \',\', $content ) );
break;
case \'bcc\':
$bcc = array_merge( (array) $bcc, explode( \',\', $content ) );
break;
case \'reply-to\':
$reply_to = array_merge( (array) $reply_to, explode( \',\', $content ) );
break;
default:
// Add it to our grand headers array
$headers[trim( $name )] = trim( $content );
break;
}
}
}
}
// Empty out the values that may be set
$phpmailer->clearAllRecipients();
$phpmailer->clearAttachments();
$phpmailer->clearCustomHeaders();
$phpmailer->clearReplyTos();
// From email and name
// If we don\'t have a name from the input headers
if ( !isset( $from_name ) )
$from_name = \'WordPress\';
/* If we don\'t have an email from the input headers default to wordpress@$sitename
* Some hosts will block outgoing mail from this address if it doesn\'t exist but
* there\'s no easy alternative. Defaulting to admin_email might appear to be another
* option but some hosts may refuse to relay mail from an unknown domain. See
* https://core.trac.wordpress.org/ticket/5007.
*/
if ( !isset( $from_email ) ) {
// Get the site domain and get rid of www.
$sitename = strtolower( $_SERVER[\'SERVER_NAME\'] );
if ( substr( $sitename, 0, 4 ) == \'www.\' ) {
$sitename = substr( $sitename, 4 );
}
$from_email = \'wordpress@\' . $sitename;
}
/**
* Filters the email address to send from.
*
* @since 2.2.0
*
* @param string $from_email Email address to send from.
*/
$from_email = apply_filters( \'wp_mail_from\', $from_email );
/**
* Filters the name to associate with the "from" email address.
*
* @since 2.3.0
*
* @param string $from_name Name associated with the "from" email address.
*/
$from_name = apply_filters( \'wp_mail_from_name\', $from_name );
try {
$phpmailer->setFrom( $from_email, $from_name, false );
} catch ( phpmailerException $e ) {
$mail_error_data = compact( \'to\', \'subject\', \'message\', \'headers\', \'attachments\' );
$mail_error_data[\'phpmailer_exception_code\'] = $e->getCode();
/** This filter is documented in wp-includes/pluggable.php */
do_action( \'wp_mail_failed\', new WP_Error( \'wp_mail_failed\', $e->getMessage(), $mail_error_data ) );
return false;
}
// Set mail\'s subject and body
$phpmailer->Subject = $subject;
$phpmailer->Body = $message;
// Set destination addresses, using appropriate methods for handling addresses
$address_headers = compact( \'to\', \'cc\', \'bcc\', \'reply_to\' );
foreach ( $address_headers as $address_header => $addresses ) {
if ( empty( $addresses ) ) {
continue;
}
foreach ( (array) $addresses as $address ) {
try {
// Break $recipient into name and address parts if in the format "Foo <[email protected]>"
$recipient_name = \'\';
if ( preg_match( \'/(.*)<(.+)>/\', $address, $matches ) ) {
if ( count( $matches ) == 3 ) {
$recipient_name = $matches[1];
$address = $matches[2];
}
}
switch ( $address_header ) {
case \'to\':
$phpmailer->addAddress( $address, $recipient_name );
break;
case \'cc\':
$phpmailer->addCc( $address, $recipient_name );
break;
case \'bcc\':
$phpmailer->addBcc( $address, $recipient_name );
break;
case \'reply_to\':
$phpmailer->addReplyTo( $address, $recipient_name );
break;
}
} catch ( phpmailerException $e ) {
continue;
}
}
}
// Set to use PHP\'s mail()
$phpmailer->isMail();
// Set Content-Type and charset
// If we don\'t have a content-type from the input headers
if ( !isset( $content_type ) )
$content_type = \'text/plain\';
/**
* Filters the wp_mail() content type.
*
* @since 2.3.0
*
* @param string $content_type Default wp_mail() content type.
*/
$content_type = apply_filters( \'wp_mail_content_type\', $content_type );
$phpmailer->ContentType = $content_type;
// Set whether it\'s plaintext, depending on $content_type
if ( \'text/html\' == $content_type )
$phpmailer->isHTML( true );
// If we don\'t have a charset from the input headers
if ( !isset( $charset ) )
$charset = get_bloginfo( \'charset\' );
// Set the content-type and charset
/**
* Filters the default wp_mail() charset.
*
* @since 2.3.0
*
* @param string $charset Default email charset.
*/
$phpmailer->CharSet = apply_filters( \'wp_mail_charset\', $charset );
// Set custom headers
if ( !empty( $headers ) ) {
foreach ( (array) $headers as $name => $content ) {
$phpmailer->addCustomHeader( sprintf( \'%1$s: %2$s\', $name, $content ) );
}
if ( false !== stripos( $content_type, \'multipart\' ) && ! empty($boundary) )
$phpmailer->addCustomHeader( sprintf( "Content-Type: %s;\\n\\t boundary=\\"%s\\"", $content_type, $boundary ) );
}
if ( !empty( $attachments ) ) {
foreach ( $attachments as $attachment ) {
try {
$phpmailer->addAttachment($attachment);
} catch ( phpmailerException $e ) {
continue;
}
}
}
/**
* Fires after PHPMailer is initialized.
*
* @since 2.2.0
*
* @param PHPMailer $phpmailer The PHPMailer instance (passed by reference).
*/
do_action_ref_array( \'phpmailer_init\', array( &$phpmailer ) );
// Send!
try {
return $phpmailer->send();
} catch ( phpmailerException $e ) {
$mail_error_data = compact( \'to\', \'subject\', \'message\', \'headers\', \'attachments\' );
$mail_error_data[\'phpmailer_exception_code\'] = $e->getCode();
/**
* Fires after a phpmailerException is caught.
*
* @since 4.4.0
*
* @param WP_Error $error A WP_Error object with the phpmailerException message, and an array
* containing the mail recipient, subject, message, headers, and attachments.
*/
do_action( \'wp_mail_failed\', new WP_Error( \'wp_mail_failed\', $e->getMessage(), $mail_error_data ) );
return false;
}
}
