This is a common issue and has definitely been solved BY USING THE RIGHT FUCKING TOOL FOR THE JOB: I.E. A DATABASE WITH AN ONLINE GUI.

You should configure Exchange to block attachments for internal messages and go thump everyone who complains.

Also, everyone who recommends Sharepoint needs a slap too.

Sergiuiuiui is right about Google Sheets.  You can tweak collaboratively, with a live message feed on the same page.  If it's anything like Google Docs, then it updates in something like real time.