Mail: Add wp_mail_succeeded hook to wp_mail.

Adds a new `wp_mail_succeeded` action in `wp_mail` after the mail is sent.  Also, adds a disclaimer to the hook's docblock, clarifying that the hook's firing doesn't necessarily mean the recipient received the mail, only that the mail was processed without any errors.

Props birgire, donmhico, johnbillion.
Fixes #53826.
Built from https://develop.svn.wordpress.org/trunk@52083


git-svn-id: http://core.svn.wordpress.org/trunk@51675 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/pluggable.php

@@ -537,13 +537,28 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 		 */
 		do_action_ref_array( 'phpmailer_init', array( &$phpmailer ) );
 
+		$mail_data = compact( 'to', 'subject', 'message', 'headers', 'attachments' );
+
 		// Send!
 		try {
-			return $phpmailer->send();
-		} catch ( PHPMailer\PHPMailer\Exception $e ) {
+			$send = $phpmailer->send();
 
-			$mail_error_data                             = compact( 'to', 'subject', 'message', 'headers', 'attachments' );
-			$mail_error_data['phpmailer_exception_code'] = $e->getCode();
+			/**
+			 * Fires after PHPMailer has successfully sent a mail.
+			 *
+			 * The firing of this action does not necessarily mean that the recipient received the
+			 * email successfully. It only means that the `send` method above was able to
+			 * process the request without any errors.
+			 *
+			 * @since 5.9.0
+			 *
+			 * @param array $mail_data An array containing the mail recipient, subject, message, headers, and attachments.
+			 */
+			do_action( 'wp_mail_succeeded', $mail_data );
+
+			return $send;
+		} catch ( PHPMailer\PHPMailer\Exception $e ) {
+			$mail_data['phpmailer_exception_code'] = $e->getCode();
 
 			/**
 			 * Fires after a PHPMailer\PHPMailer\Exception is caught.
@@ -553,7 +568,7 @@ function wp_mail( $to, $subject, $message, $headers = '', $attachments = array()
 			 * @param WP_Error $error A WP_Error object with the PHPMailer\PHPMailer\Exception 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 ) );
+			do_action( 'wp_mail_failed', new WP_Error( 'wp_mail_failed', $e->getMessage(), $mail_data ) );
 
 			return false;
 		}

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52082';
+$wp_version = '5.9-alpha-52083';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.