If setup in Azure AD properly then they should be able to email: system.Environment.UserName + “@Yourcompanydomain.com”
I have another option for you
On another note I have made a workflow to collect the current user’s email. There are limitations, though must be a minimum of 1 email in the inbox AND that email must be addressed to them directly (and not part of an email group).
Step 1: Collect Outlook Mail
Step 2: Insert For Each
Step 3: Insert Write line "item.TO.tostring
Step 4: Use this Regex pattern (preview it here)with an Assign activity to extract the email address. Like This:
CurrentUserEmail (string variable)
Step 5: Insert Write line with ‘CurrentUserEmail’.
Step 6: Validate results.
There are definitely more efficient options out there but hopefully this helps you with your needs.