One way:
n. Menu: Icon/Function
1. Add Column: Add Index Column
2. Store the Query as Query1
3. Right-click on Query1 and select Reference and change the name as Query2
4. Select the e-mail and index column and
5. Home: Remove columns/Remove Other Columns + save Query2
6. Right-click on Query1 and select Reference and change the name as Query3
7. Remove e-mail (keep the index column as the UserID)
//Ola
This is just a simple example.
There are several ways to scramble/code a email-address; shifting each letter, have a separate replacements table, etc
It's just a matter of how secure it must be.