How Does Mail “Send Later” Operate In the New Ventura?

You showed the new Apple Mail option coming in Ventura. I was wondering if I would have to have Mail running in background to use the Send Later function? At present I’m using Spark as my default email and have created templates that I schedule during the week which reside in ‘their outbox.
If the revised Apple Mail app has to be running at all times, this would defeat that option, correct? I normally close my apps b/4 I but my iMac to sleep.
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William B.