The FROM: field is set in configuration. A user cannot affect that.
When setting up a subscription the user can set the TO:, CC: or BCC: fields. As I mentioned, with limited rights and while setting up a personal subscription, the TO: field is pre-populated and not enabled to be changed. In our case anyway, what is showing up in the TO: field is the user's network ID not a valid SMTP address. It allows them to save this subscription but of course it fails when executed as the TO: address is not valid.
As an admin I went in and modified the TO: address for him but then he decided to change the delivery format and then it wouldn't let him save his changes because it was expecting the user ID value in the TO: field and he did not have rights to save to a different e-mail address. As it stands now personal subscriptions are worthless unless there is a way for them to be able to modify the TO: address or have it default to their e-mail address instead of their user ID.