Former employees are a major threat to security: How to tackle this?

Many times organization faces security issues with this, as the credentials will not be removed in most of the organizations as soon as the employee is no more in the process, but then still his account will be active many times, and at times there will be circulars which will be going from other employees and at times these things will reach to employees who are no more part of the organization or part of the project which will lead to serious issues in future, so there should be strict process automations wherein as soon as the employee finishes the project or leaves the organization the account of the employee should be deactivated, as the numbers which is suggested by the report is very low where one tracks these things, so with proper process automation data loss could be prevented and necessary action can be taken in this regard.

Access rights must be controlled.

What cannot be be changed has to be accepted! Former employees are a much greater threat than what is envisaged here because they are aware and take with them knowledge cum profile of clientele, nuances of contractual clauses, billing details and parent company weaknesses- which are of value to a business competitor. It is here that security is truly breached.  Access to emails is not an unresolvable issue, merely loop the system administrator into the employee clearance certificate with an endorsement by the system administrator that the email account has been deactivated and emails are now being redirected to the project manager. Email account management vis a vis user authentication/ access control mechanism is a minor issue compared to what an employee takes away with him, within his head on separation