Dear Sandeep,
At workplace, we must maintain professionalism. If some manager sends you derogatory mail that degrades your personal reputation, it is most unfortunate. However, filing lawsuit is too early stage. I recommend you following the procedure however, before recommending a solution, we need to know the type industry that you work in, your designation, number of persons that report to you, whether your company has approved Standing Orders.
While you may find it difficult to explain what were the contents of the e-mail. nevertheless, it is important for us to know whether the contents of the mail degraded your personal reputation. Occasionally in a feat of anger, managers send a mail. Was it a case of momentary lapse of judgement? To whom the mail was sent, on what subject it was sent and why personal reputation came in picture in the official contents of the mail? Is it really degradation of your repute or it is perception?
As a first step, you may put up application to HR with printout attached to the your application. Submission of hard copy is preferred over the soft copy. Keep duplicate copy signed by HR with you. This is called as grievance by junior employee against the manager. Give heading of your application as "Grievance Against __________ (designation of the manager)" or "Grievance Against the Reporting Authority".
On receipt of your application, your HR will conduct the investigation. If you are not satisfied with the outcome of investigation or if you are not satisfied with the quantum of the punishment awarded to the defaulting manager, you may put up second application to the highest authority of your company asking for the review.
If you are not satisfied with the outcome of the review then you need to take the matter out of your company. Find out the labour office of your area. Approach the Labour Officer (LO) and explain your problem in sequence. Carry with you evidence of all of types including proof that you are employee of your company. On listening your complaint, LO might issue letter to your company. This is called as industrial dispute. On a specified day, he will call both the parties, listen viewpoint from both the sides, and give his verdict. If you are not satisfied with the verdict then then you may send the notice from the lawyer. Your lawyer will give you further guidance as such.
Final Comments: - While I have given above the procedure for settling the grievance, I recommend you settling the matter without taking it too far. It could impinge on your career. Taking on manager could prove risky. Managers are representatives of the management. Incensed by your application, you management might fix you in some or other matter. Therefore, take into account the support from the top that your manager enjoys.
Thanks,
Dinesh Divekar