Alerts trigger a WP_Error when no email addresses are set

Hi!

We’ve noticed that the Sucuri plugin still tries to send email alerts even when there are no email addresses in the list of recipients. And, when sending a “Test Email” from the Alerts settings page, it will reload the page and say it was sent successfully, which of course cannot be true.

This is triggering a WP_Error when it happens (presumably because Sucuri is calling wp_mail but not providing a To: address.)

Below is a WP_Error object that we logged; this dev site happened to be using the Fluent SMTP plugin (Configured to send outbound mail through Mailgun), but the issue is the same regardless.

WP_Error Object
(
    [errors] => Array
        (
            [wp_mail_failed] => Array
                (
                    [0] => Mailgun API Error
                )

        )

    [error_data] => Array
        (
            [wp_mail_failed] => Array
                (
                    [to] => Array
                        (
                            [0] => 
                        )

                    [subject] => Sucuri Alert, dev.local, Test Email Alert, 127.0.0.1
                    [message] => 
Event: Test Email Alert
Website: https://dev.local
IP Address: 127.0.0.1
Reverse IP: dev.local
Date/Time: July 25, 2024 4:21 pm
User: andrew

Message: Test email alert sent at July 25, 2024 4:21 pm

                    [headers] => Array
                        (
                        )

                    [attachments] => Array
                        (
                        )

                    [phpmailer_exception_code] => 400
                )

        )

    [additional_data:protected] => Array
        (
        )

)

Thanks!