Must or Should?

[Sush]

The receptionist MUST answer courteously the questions of all the callers

The receptionist SHOULD answer courteously the questions of all callers

Which one of the above two sentences is correct? Also, explain me when must is used and when should is used? I need the difference between the two.

Thank you:)

[Mister Micawber]

Use 'should' for laying down guidelines. Save 'must' for absolute laws.
_________________
Native English teacher at Mister Micawber's

[Sush]

Thank you so much :)
So, "The receptionist MUST answer courteously the questions of all the callers" is the correct answer, right?

[Mister Micawber]

No. 'Should'... if you wish to keep your employees and operate in a modern manner.
_________________
Native English teacher at Mister Micawber's