Great points, especially on deliverability - that's the biggest trade-off with BYOSMTP. You're right that managed providers have better reputation management, which is why our hosted service is positioned as the primary offering. The open-source version serves a different need: developers who want full control or have compliance requirements that prevent using third-party platforms.
On market positioning, I think there's still room between "build your own email system" and "pay $200+/month for enterprise features you don't need." Our target isn't competing with MailChimp for high-LTV businesses, but serving the gap where small businesses outgrow basic tools but aren't ready for enterprise pricing. That said, your "Mom test" concern is valid. We're validating this with real users to ensure we're not just building for ourselves.