Difference between "delivery person" and "mail carrier"

[Olena]

English Grammar Tests, Elementary Level

ESL/EFL Test #126 "Real Life: Occupations (1)", question 10

My uncle is a .......... He delivers mail to people everyday. He works for the government and gets a lot of exercise because he walks to individual mailboxes on his daily route.

(a) delivery person
(b) mail carrier
(c) cashier
(d) plumber

English Grammar Tests, Elementary Level

ESL/EFL Test #126 "Real Life: Occupations (1)", answer 10

My uncle is a mail carrier. He delivers mail to people everyday. He works for the government and gets a lot of exercise because he walks to individual mailboxes on his daily route.

Correct answer: (b) mail carrier

Your answer was: incorrect
My uncle is a delivery person. He delivers mail to people everyday. He works for the government and gets a lot of exercise because he walks to individual mailboxes on his daily route.
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Hello,
Could you explain the difference between "delivery person" and "mail carrier" and, please, give some examples when it is better to use them.
Thank you in advance
Olena

[Mister Micawber]

.
'Delivery person' is not a natural English collocation. and would not apply to mail delivery if it were.
.
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Native English teacher at Mister Micawber's

[Olena]

Thank you, Mister Micawber
I have never met this word combination bebore but now I know it is not natural.