I love these kind of articles. But I think it's a bit weird that most devs choose to horizontally scale at the data persistence layer, instead of the applicatio

I love these kind of articles. But I think it's a bit weird that most devs choose to horizontally scale at the data persistence layer, instead of the application layer. And that they choose a SQL database to basically store just text blobs. As this is a mail app, and users doesn't need to read each others private messages. I would put say 100 users per (virtual) server and also store the data there. And have a simple traffic router.