Sentence: The company has branches/facilities throughout the country and holds...

The company has branches/facilities throughout the country and holds the monopoly of the delivery of small mail, like letters.

hi,
is this sentence fine, please?
thanks.

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I think ‘monopoly on’ is more usual. The term ‘small mail’ is unfamiliar to me, and nothing on the first couple of pages of Google results suggests that the phrase means ‘letters, etc’.
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thanks.
how would a native speaker write this text, please?
Thanks again.

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I am afraid that I don’t know a term to refer to letters but not packages. I suppose that I would write:

The company has branches/facilities throughout the country and holds the monopoly on mail delivery.

thanks a lot.
in this case the monopoly is on the mail that can be enclosed in envelops, such as phone bills and things like that. the monopoly also aplies on letters but virtualy nobody send letters these days, right?
I found the expression ‘‘small mail’’ on the web and that’s why I used it.
thanks again.