In informal letter whose address is written: one who is writng or one to whom we are sending i.e, the writer's address or reciever's address
We write our own address while writing an informal letter. We kindly request you to follow the link given below to study the format and samples of an informal letter:
https://www.meritnation.com/cbse/class10/studymaterial/english/writing-section/informal-letter/834_4489_11124#slide1_introduction
https://www.meritnation.com/cbse/class10/studymaterial/english/writing-section/informal-letter/834_4489_11124#slide1_introduction