Service of bills for charges or notice of demand by ordinary post.

Notwithstanding anything contained in sections 100 and 101 a bill for any charges or a notice of demand may be served by sending it by ordinary post with a prepaid letter under a certificate of posting addressed to the appropriate person specified in section 101 at his last known place of residence or business and in proving the service of every bill or notice so sent it shall be sufficient to prove that the letter was properly addressed and posted under a certificate of posting.