Click on the 
menu at
the top of the screen
To deactivate an existing Workflow Manager Mailbox you need to have Manage Workspace Mailbox - Workspace Level Privilege.
The following steps should be used to deactivate an existing Workspace Mailbox:
Click on the menu at
the top of the screen
Select Manage Workspace Mailbox
Click on the Workspace Mailbox name displayed in the list for which you want to change the configuration
Mark the check-box of Inactive as ON
Click on Save to deactivate the Workspace Mailbox
Once deactivated, no further mails can be sent to the
mailbox. However the mails published earlier will not be affected and
will still continue to be available.
Useful Links: