When creating campaigns they are automatically public (and hence viewable in the archive); is it possible to change it such that the default option is 'Hidden' and then they can be made public after the fact; effectively allowing opt-in to the automatically generated archive?
Hope this is clear.
Unfortunately it's not possible to make sent campaigns hidden by default. They must be manually hidden.
When you go to the Reports tab, you will see Visible to clients next to each sent campaign. Toggling this to Hidden from clients will hide it from the newsletter archive too. However, if this is for your client's account, they will not be able to view the reports of hidden campaigns.
If that's not practical, you'll need to manually create a newsletter archive using short URLs for selected campaigns. Just click the Share button when viewing a report to get this URL.
That's fine. No, that process is not practical; we will need to take a manual approach.