do you need to put return address on mail
Return address The return address is not required on postal mail. However, lack of a return address prevents the postal service from being able to return the item if it proves undeliverable; such as from damage, postage due, or invalid destination. Such mail may otherwise become dead letter mail.[2]
Blind carbon copy It is common practice to use the Bcc: field when addressing a very long list of recipients, or a list of recipients that should not (necessarily) know each other, e.g. in mailing lists.[2]