[openmind]

When you say share do you mean deliver a copy of the email? If so there a couple of ways it can be done but the 3rd party receiving the email could reply without you knowing.

One way is to setup a MRA (Multi Recipient Address) for the email account so it fires a copy of the email to xx people.
Second way is using a store and forward so the email is store on the server as normal but also forwards a copy to another email address.

Does depend on the host though and if they support these features.