Validity of documents in case of services

What are legally valid documents in case of providing any kind of media service like advertisments in print media , electonic media ?

is email confirmation legally valid or binding for any  type of services ?

does contract in case of above needs to notarise or registered under registration act.

normally i have seen many cos never notarise or register their orders or contracts in businesses most of the documents are not in proper format.

Thanks 

David