Acknowledgement Letter is a letter where the work or the effort of an individual or a group of individuals is recognized. But recognized not in monetary terms but only in terms of agreeing that the particular letter/assignment/project has been received. An Acknowledgement Letter can also be given for receipt of money in some form. The beauty of an Acknowledgement Letter is that it can be written by an organization to an individual or vice versa.
An Acknowledgement Letter may or may not necessarily be an official letter. A sister sends the sacred thread of ‘Rakhi’ to her brother and the brother acknowledges receipt of the mail through a return AcknowledgementLetter. An employee of an organization sends a letter through courier outside the organization gets an Acknowledgement Letter from the recipient confirming that the courier has been received.
In earlier times when pigeons were used as a mode of communication, sending a letter back through the pigeon was an Acknowledgement Letter. Then came the times of registered letters sent through the postal department. These letters went with ‘Acknowledgement Due (AD)’ cards, which needed to be signed by the recipient and were then delivered by the postal department to the sender. Now these are times of couriers where the POD or Proof of Delivery is an Acknowledgement.
Since letters can be delivered by hand or post they can be acknowledged by return post or by signing on a copy of the letter delivered by hand.