Is it obligatory to convey salams if a person requests that, and is one sinful for intentionally not conveying them?

If a person says to another: "Convey my greetings to so-and-so," this is a trust (amanah) that must be delivered, provided that the person accepts the responsibility of bearing this trust. If the conveyor commits to delivering the greetings, then it becomes obligatory upon him to do so, in accordance with the Almighty's saying: (Indeed, Allah commands you to render trusts to whom they are due) An-Nisa/58. However, if he does not commit to it, then he is not obligated to convey the greetings.