> I'm not sure how much should I trust a vps host. I can mess around with encryption all day long but they can compromise my mail server without me ever knowing.
Basically, you can't. It all depends on your threat model.
Maybe have a look at cryfs and encfs ? One of them is `optimized` for always on syncing and small chunks (can't remember which) and the other is deprecated (or a third one, can't remember at the moment).
But yeah, if you have a business... don't self host too much sensitive stuff, delegate if you can.
Basically, you can't. It all depends on your threat model.
edit: https://owncloud.com/features/end-to-end-encryption-2/ owncloud community and standard edition don't have e2e