I have been trying to send an email (from Outlook 2007) with an attached
Excel file (saved as Excel 97-2003 Workbook), to a group of people who likely
have different versions of Microsoft Office (e.g. some have Office 2003).
The attachment is coming across jumbled and unreadable.

The Excel file ends with 'xls' in the attachment.

Ive also tried formatting the email as plain text, but those trying to open
the attachment /view the email still receive it as jumbled text. How can I
fix this so that all recipients in the group, possibly with different
versions of Excel can all download the attachment and work with it as
intended?