If you click the link I provided it takes you to the app on the google play store which also links to their website and is registered under Lavabit LLC. Additionally if you search for the app it is open source and attached to their GitHub account.

Currently the app doesn't have a lot of the functionality I require like split tunneling but I have great respect for Lavabit seeing as they were one of/if not the first encrypted email service to arrive, utilised by Edward Snowden, and they decided to close shop rather than divulge keys to the gov when requested. Plus they are currently working on a new encrypted email protocol which I would like to utilise when available.

I won't be using Proton as they seem to follow Apple's premium pricing philosophy and require account creation. Mullvad is more respecting of privacy via not needing an account but the only anonymous way I see of paying for their service is by sending cash to them via post which isn't very economical.

Was planning on hosting from my home server. Will definitely read up on those protocols and the recommendations. Have certificates and domain routed through Cloudflare. ISP is optus but it's not a business connection so that could be problematic r.e: spam filters :/

Sweet thanks. Only other thing I've been concerned about is opening ports into my network. Anything you've done to increase the security with this in mind?

By VPS I assume you mean I would need to spin up a new Ubuntu VM instead of say run it in docker along with a bunch of other services. Or are you saying I'd need to have a completely separate barebones machine?

I'm currently running OPNsense virtualised in Proxmox. It's a little confusing if you haven't run a custom firewall before but the setup was relatively simple and works flawlessly now that I understand it a bit better. The only downside being if you are running it on the same machine as your services need to restart your network will go down as well.