I came across this example on WordWeb while going through the meaning of the word 'avalanche'.
the program brought an avalanche of mail (Just like "a group of
I'm quite sure it should be mails. Kindly confirm.
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Mail is a uncountable noun, as in: "There is a lot of mail in that mailbag."
Therefore, it would be an avalanche of mail (but an avalanche of letters).
We would say, "Would you please take this mail down to the mailbox?" even if there were three pieces of mail to take.