Existence of course of business when relevant
16.  When there is a question whether a particular act was done, the existence of any course of business, according to which it naturally would have been done, is a relevant fact.
Illustrations
     (a)  The question is whether a particular letter was despatched.
     The facts that it was the ordinary course of business for all letters put in a certain place to be carried to the post, and that that particular letter was put in that place, are relevant.
     (b)  The question is whether a particular letter reached A.
     The facts that it was posted in due course and was not returned through the Dead Letter Office are relevant.