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You don't need an IP from Google to host your SMTP (which I've been doing for ages). Residential or dynamic IP is a no-go, but any server-designated IP subnet will work assuming it has proper SPF, DKIM, DMARC set up. I agree kind of removes the use case for the Helm which, if I understood correctly, is hosted at home, but hosting your SMTP on a broadband is a bad idea anyway.