Meaning of service by post

Where any Himachal Pradesh Act authorises or requires any document to be served by post, whether the expression "serve" or either of the expressions "give " or "send" or any other expression is used, then, unless a different intention appears, the service shall be deemed to be affected by properly addressing, pre-paying and posting by registered post, a letter containing the document, and, unless the contrary is proved, to have been affected at the time at which the letter would be delivered in the ordinary course of post.