an HTML file is NOT an Excel file, right?

we use an application that has an "export to excel" feature that doesn't work on PC's that done have outlook express installed.

i know, you're thinking "WTF does outlook express have to do with excel files?"

i asked the same thing, and here's what i found:

• the file being generated is actually one o开发者_StackOverflow社区f those Microsoft Single File Web Pages (.mht) and NOT an excel file
• you need to have outlook express installed to actually view a .mht file.

i've explained to their support people that just because you can slap a .xls on a file and excel will open it does not mean its an excel file, and does not mean that this is the right way to do it.

how would you explain that this is not proper?

Many people (especially managers) confuse Excel files with reporting files. In my opinion, a file is only qualified as an Excel file if it meets all of these conditions:

1. Is a spreadsheet formatted in one of the many Microsoft Excel formats.
2. Can be opened in the most recent version of Microsoft Excel.
3. Is editable in Microsoft Excel.

In your case, I'm guessing only condition #3 is met, so it's no Excel file. But your support people may still call it a reporting file.

If a clean Windows image with only Excel installed can't open it, then it isn't in Excel format. Period.

If a Windows machine with Outlook Express, but without Excel can open it (if you change the extension) then it can't be an Excel file. I'd combine that with Ignacio's suggestion for a slam-dunk.

Plus, surely if it's MHT, then you can't actually do spreadsheet operations on it? Or am I misunderstanding how it works?

I don't think your statements are correct. Excel (2007) has import and export filters for single-file HTML documents (.mht) even if there is no Outlook Express installed. However, this is not a native format and worksheet features such as formulas cannot be retained (see http://office.microsoft.com/en-us/excel/HP100141051033.aspx#7)

So what you should make clear to your customers is that there is a difference between an applications native file format and a format which isn't designed to contain spreadsheet functionality and that is only supported via an import/export filter.