Which mail server allows you to view user mail?

Question

Mail server

We need a mail server that can view user mailboxes (lotus domino can do this, but I haven’t mastered something with it yet)
ps preferably on Windows
pps if it would be good without a domain at all

Answer 1

No.
This functionality is screwed from above. And if the mail is encrypted - then only to those who have certificate keys. In eksch it is. In any linux server, you can view mailboxes directly (but this is very inconvenient).
Do not forget that you are obliged to warn the user that the mail is being viewed.