Remove Inbox Rule via Gmail
Log in to the affected user's Gmail account
Go to Settings → See all settings
Go to the "Forwarding and POP/IMAP" tab and check for any suspicious forwarding addresses. Remove them if found
Go to the "Filters and Blocked Addresses" tab and check for any filters that might be forwarding emails. Delete them if found
Suspend a user via Google Admin Console
Go to the Google Admin console → Users → Find the user
Click on the user's name to open their account page
Click Suspend user
To confirm, click Suspend
Password Reset via Google Admin Console
Go to the Google Admin console → Users → Find the user
Click on the user's name to open their account page
Click Reset password
Choose an option to generate the password automatically or to create it yourself
(Optional) To require the user to change their password the next time they sign in, click "Ask for a password change at the next sign-in"
Click Reset
Save the new password in a secure location
Reset user's sign-in cookies via Google Admin Console
Go to the Google Admin console → Users → Find the user
Click on the user's name to open their account page
Click Security → Sign-in cookies → Reset
Re-enable the User Account via Google Admin Console
Go to the Google Admin console → Users → Find the user
Click on the user's name to open their account page
At the top left, click Reactivate
To confirm, click Reactivate