[Users] How to hide sender IP address and host name?

[Removed GDPR]

> The info is sent when using webmail, only the IP number is their IP
> number and not yours.

I know that. I guess for the sake of clarity I need to ask then: How to
send email without revealing the sender's IP address? Is it possible
for example for the client and/or server to be configured in a way
which sends only the IP address of the server but not that of the
actual computer from which the message is sent? (I suppose Gmail is
doing something like that)

> You can use the 'Domain name' option on the 'Advanced' page of the
> Account preferences to give a false host name.

That works for the host name, thanks!