I'm looking for an e-mail program that can open an .xls attachment
automatically.

Why do I have such an odd request? I'm experimenting with a computer
that is connected to a projector, this computer is showing Excel
files.
I want to be able to send a mail to this computer and the attached xls
file will be automatically executed.
It is difficult to find an email-client that supports this because of
the virus risk.
I'm not interested in ideas how I can solve the problem by any other
way than with an email program.
(MS Outlook or Outlook Express doesn't support this)

Thanks!