Reporting manager has mishandled the case.
Personal note depends on his integrity and value for his words.
What type of items was left out before employee quit?
Employee knows he is not entitled for certain incentives and is bargaining to secure the same.
Writing to new HR may mean employee may react further adversely.
New HR may not take it too seriously also
So assess what exactly is the input you need from this person and whether it is worth wasting time on bargaining.?
Thought i agree on the point that we cannot do anything on monetary terms because the F&F is already done. However we are not at all giving his incentives as he has not completed 1 year as per the norms
Also, the motive to drop mail to his current company HR is only that such kind of employees can be harmful to any company in future. And they should taste this lesson to not repeat such kind of practices in future.
You may first put a diplomatic email to be on the records just in case it snowballs into a controversy at a later stage or worse still becomes a legal dispute. It has to be shown that you made all the efforts from your end to get the above done in a smooth manner but were constrained to issue notice /send note to the present employer etc. Hope you will get it sorted out amicably as the ex-employee might be scared that his ex-employer may not pay him once the handover is done in full. Was there any issues of similar sort earlier? See that you do not damage your company reputation in trying to solve the issue aggressively.
When that employee had resigned, the manager should have made him to properly hand over everything. Moreover, the manager should have contacted you (HR) if something was incomplete prior his relieving procedure. The employee served his notice period, has been issued relieving letter, experience letter and F&F is done. That shows he has done his part well - at least document wise.
Learning from the lesson, inform all the HODs to take HR in loop for charge hand over issues. They should not open up issues post relieving.
Dropping mail to that employee's new company will not serve the purpose, as in that case you will have to produce facts and figures and there is nothing in writing between manager and employee. The employee could easily raise his hands saying his past company is troubling him for no reason.
With regards to incentives, you have a point. If rules state one year completion period, in no case employee can claim it.
It shouldn't be, you all are imagining a fight about something that was easily achievable with a request.
Give it a try. Use your HR skills.
The root cause of the problem is half job by the manager. More than exited employee, his manager is responsible. He should have been thoughtful enough to allow his subordinate to quite without complete hand over. That manager had verbal agreement with the subordinate holds not ground. He should have been thoughtful enough of consequences if his subordinates turns unfriendly. I recommend you taking action against the manager for doing incomplete work. This is a failure of managership.
Anyway, you may tide over current challenge nevertheless, hereafter you need to obtain two undertakings. One is from the HOD/Reporting Manager stating that the exiting employee has handed over charge of his/her duties completely and nothing is left. The second undertaking is from the exiting employee for giving proper responses to the queries raised by the employees working in his department.