An informal letter is a non-official letter that we usually use to write to our friends, family or relatives. These letters are personal letters that are not used for official purposes. There could be many reasons for which we write these letters to our family and friends. informal letter example For example, if we want to inform them about our achievement in school or college, then we write them a letter to spread our personal news.Since, the letter is informal thus the salutation is usually given by ‘Dear’, such as Dear (name of friend/name of uncle or aunty) or Dear Father/Mother, etc. Unlike formal letters, you don’t have to mention the subject line for informal letters. But the address of senders and receivers of the letter has to be mentioned necessarily.Get Other Types of Letter Writing like Formal, Informal and Different Types of Letter Writing Samples.