Letter Writing is one of the simplest things to learn! But most of us forget that this is not about writing a single letter only. This Simple-Special Art of Communicating the 'Persuasive' content demands precision, accuracy and care. Here is the format Podcast and Image for you to refer.
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.