The right way to open CSVs in Excel is:
Data -> From Text -> Browse to your csv -> Delimited -> Comma -> Next -> Select Text formatting for columns with leading zeroes -> Finish
You can either send xlsx with format or csv without format. If this would be disabled then we'd have another group of people complaining that their dates from CSV are not parsed.
and to enforce that, remove the file association which opens .CSV files in Excel by default. If every machine opened CSV files in notepad a huge percentage of 'Excel' problems would just go away. It could be worse though, try opening and saving a CSV in Word and see what that does.
You can either send xlsx with format or csv without format. If this would be disabled then we'd have another group of people complaining that their dates from CSV are not parsed.