• It was open-sourced a long time back after the dev felt the number of users who bought and the amount of time he spent didn’t feel profitable.
• I tried using it, but stopped moving all my financial data as it can’t handle multiple currencies.
• The web interface on mobile browsers was very basic, not sure it’s still the same.

Wireguard + pihole?

What I feel is that you need do is to compare the cost of power supply vs hardware then choose whichever is cheaper.

A good read about self hosted email servers: https://news.ycombinator.com/item?id=32715437

If you are going to use it within your family members it will be fine, but not with other users who uses corporate provided email services.