Section 16 of Evidence Act "Existence of course of business when relevant"
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
dispatched.
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.
Section 17 of Evidence Act "Admission defined"
An admission is a statement, 8A[oral or documentary or contained in electronic form], which suggests any inference as to any fact in issue or relevant fact, and which is made by any of the persons, and under the circumstances, hereinafter mentioned.
What is when facts not otherwise relevant become relevant Section 11 of Indian Evidence Act 1872
What is Admission- by party to proceeding or his agent Section 18 of Indian Evidence Act 1872