That 'obligatory' (why?) reference is not relevant in this case since self-hosted mail is at least functionally identical to 'cloud'-hosted mail, in practice often superior to such while the proposed alternative to Dropbox is not [1].

If you can not or do not want to host your own things, fine, that is your right. That does not mean that your own inability or unwillingness to do so translates to others. Some people never cook for themselves, they always eat out. It would be just as easy to present an 'obligatory' reference to 'flour + yeast + water + oil + tomatoes + garlic + mushrooms + bacon + olives + cheese = pizza', implying that those who think you can make your own are deluded. It is a good thing that most people realise cooking your own food is a good thing to (be able to) do, it would be a good thing if more people realised it is possible to 'self-cook' your own services, either from some instant package ('click here to install your own mail server') or by cobbling together the needed parts.

[1] ...but a self-hosted instance of e.g. Seafile or Nextcloud is functionally superior to Dropbox and, at least for Nextcloud, is starting to become supported in third-party products so self-hosting still wins in the end