You may refuse to receive a note, from a minor, (if you have not made an associate of him); one that has been posted; one that has been publicly disgraced without resenting it; one whose occupation is unlawful; a man in his dotage and a lunatic.

There may be other cases, but the character of those enumerated will lead to a correct decision upon those omitted.
If you receive a note from a stranger, you have a right to a reasonable time to ascertain his standing in society, unless he is fully vouched for by his friend.
4.

If a party delays calling on you for a week or more, after the supposed insult, and assigns no cause for the delay, if you require it, you may double the time before you respond to him; for the wrong cannot be considered aggravated; if borne patiently for some days, and the time may have been used in preparation and practice.
Second's Duty of the Party Receiving a Note Before Challenge Sent.
1.

When consulted by your friend, who has received a note requiring explanation, inform him distinctly that he must be governed wholly by you in the progress of the dispute.

If he refuses, decline to act on that ground.
2.