I have done mailinabox.email and recently I switched to mailcow-dockerized like optmzr. By default, they both apply strict security practices so you won't have

I have done mailinabox.email and recently I switched to mailcow-dockerized like optmzr. By default, they both apply strict security practices so you won't have an open relay, worried about domain masking etc. Either are about a day to set up and its mostly DNS.