Meaning of service by post

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