Official Communication is done through Inter and Intra-Office Communication Tools. Notice, Circular and Memo are the Intra-Office (Within the organisation) tools. Letters come in the Inter-Office Communication category. Block Format of Letter Writing is used these days for Official Communication.
As Letters are Inter-Office Communication Tools, Persuasion plays an important role. It sometimes seems stereotyped, yet these components are necessary. We must remember that Letters are written for the Recipient, not for the writer. Thus, the contents are planned as per the receiver's requirements. A PODCAST and the Related Format is shared below: