Disable sending .ics files outside our orginisation

Our company uses Echange 2003 server and Office 2010 and we want to send meeting invites outside our organisation.

However when we send the invite they all get a meeting.ics file. This is a problem because not everyone can open .ics files. We would like to send it as plain text in-staid of the .ics file.

The "send iCalendar outside your organisation" is checked off and I tried to send the meeting mail "as plain text"

I hope I've given enough information,

Jonne