I’m not sure if mailbox encrypts their calendar and contacts. I know tuta and Proton do but I self host that stuff anyway so I don’t care.
I use to selfhost everything, including email. However, emailing anyone from my domain I was 99% of the time in the spam list if it went though at all. I got fed up and paid someone to do it for me.
So really, I just need to host my own instance to see votes. Nice.