function bp_nouveau_ajax_messages_send_message() {
	$response = array(
		'feedback' => __( 'Your message could not be sent. Please try again.', 'buddypress' ),
		'type'     => 'error',
	);

	// Verify nonce
	if ( empty( $_POST['nonce'] ) || ! wp_verify_nonce( $_POST['nonce'], 'messages_send_message' ) ) {
		wp_send_json_error( $response );
	}

	// Validate subject and message content
	if ( empty( $_POST['subject'] ) || empty( $_POST['message_content'] ) ) {
		if ( empty( $_POST['subject'] ) ) {
			$response['feedback'] = __( 'Your message was not sent. Please enter a subject line.', 'buddypress' );
		} else {
			$response['feedback'] = __( 'Your message was not sent. Please enter some content.', 'buddypress' );
		}

		wp_send_json_error( $response );
	}

	// Validate recipients
	if ( empty( $_POST['send_to'] ) || ! is_array( $_POST['send_to'] ) ) {
		$response['feedback'] = __( 'Your message was not sent. Please enter at least one username.', 'buddypress' );

		wp_send_json_error( $response );
	}

	// Trim @ from usernames
	/**
	 * Filters the results of trimming of `@` characters from usernames for who is set to receive a message.
	 *
	 * @since 3.0.0
	 *
	 * @param array $value Array of trimmed usernames.
	 * @param array $value Array of un-trimmed usernames submitted.
	 */
	$recipients = apply_filters( 'bp_messages_recipients', array_map( function( $username ) {
		return trim( $username, '@' );
	}, $_POST['send_to'] ) );

	// Attempt to send the message.
	$send = messages_new_message( array(
		'recipients' => $recipients,
		'subject'    => $_POST['subject'],
		'content'    => $_POST['message_content'],
		'error_type' => 'wp_error',
	) );

	// Send the message.
	if ( true === is_int( $send ) ) {
		wp_send_json_success( array(
			'feedback' => __( 'Message successfully sent.', 'buddypress' ),
			'type'     => 'success',
		) );

	// Message could not be sent.
	} else {
		$response['feedback'] = $send->get_error_message();

		wp_send_json_error( $response );
	}
}