Ok, I can understand your concern now but I feel like you’re basically saying that mail and self-hosting in general shouldn’t be streamlined at all and be super complex. Because your recommendation puts a lot of the security burden on the end user building their setup of various best-of-breed solutions. You would then yourself have to ensure all inter solution communication is secure as well as deploy every solution securely. Whereas with a all-in-one it’s generally on the Developers and the larger FOSS community to ensure the package is secure internally and the end user is only responsible for the deployment (i.e. that they follow the instructions and have reasonable security on the server they deploy to). Theoretically if an end user is very bad at security then your recommendation doesn’t end up with a more secure solution over all, it would be just as easy to compromise as the all in one, if not easier.