Continued a bit: (please cherry-pick)

Continued a bit: (please cherry-pick)
- please let the application and not the validator decide what to do with already registered or unregistered email addresses.
- the validator should only validate (against regex) and not make sure (means control) that the valid email address is okay to use for the requested action.
- else there is a double-check and the validator will come first with non-localized messages

Signed-off-by: Roland Häder <roland@mxchange.org>