noun
BAD : It takes seventeen trees to produce one ton of junk mails.
GOOD : It takes seventeen trees to produce one ton of junk mail.
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Mail (= letters and parcels) is an uncountable noun: 'Has there been any mail today?'
noun
BAD : It takes seventeen trees to produce one ton of junk mails.
GOOD : It takes seventeen trees to produce one ton of junk mail.
◆◆◆
Mail (= letters and parcels) is an uncountable noun: 'Has there been any mail today?'
Longman Common Errors English vocabulary. Английский словарь распространенных ошибок Longman. 2012