My System:
Release 7.2.3_GA_2872.UBUNTU8 UBUNTU8 FOSS edition.
But for all versions the same problem.

In the admin panel there is under "global configuration -> MTA" the option "add X-Originating-IP to mail". This option is per default on.
If this is on the original IP address of sender will be added as an extra option to the mail header.

I see two problems there:
Privacy. Why should the receiver see the original IP address?

Spam. Many spam filters (Zimbra included) use this option in a wrong way. They say the mail was sent from a private range that is on a anti spam list and mark this mail as spam.

So why is this option per default enabled?
What are the positive effects of this option (I have really no idea in which situation the original IP is useful)?

Is it required to restart the zimbra services if I disable the option?