What I want is that all emails sent to/from
email@example.com are copied to
firstname.lastname@example.org. The configuration solution must not be modifiable by
user1 (due to that requirement I think any solution that includes the creation of a filter in the
user1 account won't suit, unless a filter in
user1 account that
user1 can't delete), and if the configuration is hidden from
user1 all the better.
Here is the doc to do that.
The Content compliance setting enables you to specify what action to perform for messages based on predefined sets of words, phrases, text patterns, or numerical patterns. The content compliance setting scans messages for content that matches one or more rules that you configure within the setting. You can choose whether these messages are rejected or delivered with modifications -- for example, to notify others when the content of a message matches the rules that you set.