Furthermore, the thing that complicates the current discussion is with email services in particular, so much depends on reputation and avoiding getting on block

Furthermore, the thing that complicates the current discussion is with email services in particular, so much depends on reputation and avoiding getting on block-lists. There's also the header wizardry that has become a requirement for interoperating with a lot of large email servers that isn't required for using the protocol but is practically required to ensure delivery. On the flip-side of that, there are those who want the extra amount of customization that can only truly come from owning the entire stack. Or perhaps they already have a high-reputation IP address they have been sending from for years, and a self-hosted solution is necessary to continue with that (barring some transfer of that IP address to the operation of another company). In that case, calling this self-hosted is being disingenuous. In some ways I see the dependency on SES (or other third party provider) as being a benefit for email hosting, especially for a new venture/property. It's why there is some value in depending on other examples of managed services. But I would be clear about that and not call it self-hosted.