Why does the BeforePostingSendMail event not fire when sending Bitrix?

Question

1C-Bitrix

Found the BeforePostingSendMail event
Added the corresponding code to init.php:

AddEventHandler("subscribe", "BeforePostingSendMail", Array("MySubscribeClass", "BeforePostingSendMailHandler"));
class MySubscribeClass
{
    function BeforePostingSendMailHandler($arFields)
    {
    $arFields["BODY"] = str_replace("#NAME#", "CustomData", $arFields["BODY"]);
    return $arFields;
    }
}

In the mailing template
имя: #NAME#
I expect to see in the letter instead of #NAME# - CustomData, but the value is not changed.
I assume that the event itself does not work. How to make it work?
Bitrix version 18.1.8 Business edition, php 7.1.29.