Email can't guarantee E2EE without a block cipher tool like GPG. Even if your provider stores and transmits only encrypted email data, once sent it does not maintain that guarantee while being passed by another entity's MTA.

If you email google, google gets to do whatever googly stuff it would like to do with its algorithm. If you email exchange, roundcube, ISP, hotmail, it could wind up being archived to tape, or simply be sitting for a long time in some unencrypted mail spool, maybe in a public cloud. If you selfhost, you would be forgiven if you find you have made a mistake or simply got pwned.

I've never selfhosted email, but I understand it is a lot of work to set up if you aren't familiar, and while maintenance is okay once you get rolling, there are occasional emergencies or hiccups that require intervention.

Aside from being much slower, regular mail is quite better since you can easily inspect the envelope for evidence of tampering, while email will be imperceptibly copied.