Dear Saunak,
You have not mentioned the context under which you have raised this query. Is your query from the employer's point of view or is it that as an employee you have come across with some actus reus of someone and you wanted to bring it to the notice of the management under but at the same time you want to protect your identity?
Other than suggestion box or survey, the only method left is writing to MD anonymously and sending the details by courier. However, many times, rather than reaching to MD, letters of this kind find their way to the trash can.
The anonymous word in your post brings to fore the crux of the matter. Whether you have written post from the viewpoint of employer or employee, this very word suggest that employees are wary of giving suggestions or feedback to their seniors. Therefore, what is important is to create a culture where juniors give feedback without fear of reprisal. If some employee is engaged in insalubrious activity, and if other employees look at the other side, how much loss the company could be incurring that cannot be estimated.
You wanted to engage the employees by creating a channel for upward communication. However, essence of employee engagement lies in open and transparent communication. When employees wanted to hide under the guise of anonymity, it symbolises their lack of trust. It also symbolises they have fear of conflict either with their peers or superiors. Otherwise these employees could be well wisher of the company but do not want be open whistle blower. Why do they wish to blow their whistle privately is a point to ponder!.
Thanks,
Dinesh Divekar