Do you support sending to email address with raw IP address or .onion domain as the domain part? Eg:

  test@192.0.2.4
  test@[2001:0DB8::0004] # or possibly
  test@2001.0DB8..0004
  test@l5satjgud6gucryazcyvyvhuxhr74u6ygigiuyixe3a6ysis67ororad.onion