Lets talk about Own-Mailbox again (home-hosted email service)

The video and "how does it work" don't really explain much, I think.

They claim to protect meta-data because everything is behin Tor hidden services. To receive actual mail, though, they set up a central SMPT/Tor-Proxy. So that proxy knows the meta data (and in case of unencrypted mail, the content) and the hidden service associated with that meta-data.

So even though everything is open source and open hardware, you still have to trust this central proxy, don't you?