[dba-Tech] Securing Excel File to avoid E-mail forwards

Hi Group
 
On a daily basis I send 1 Excel files to about 120 recipients using
E-mail.
The file contains confidential information and is also popular
information for press and other third parties, but may not be disclosed
before the rightfull owner (all of the 120 recipents) decides to do/or
not so for his or here data.
I'm sure this E-mail gets forwarded to other parties that may not
receive this information.
Are there any means today to avoid forwarding this Excel file or atleast
to track back who has forwarded it?
 
I would like to hear suggestions from "cheap to expensive", from "helps
a bit to helps a lot".
 
Some additional remarks:
-I would like to avoid sending 120 slightly different Excel files
instead of "1 for all".
-Excel file is obligatory.
-Normal Excel file operation for the recipient, changing, adding,
deleting content etc.
-Avoiding 24x7 server availibility at my office for on-line verification
or logging or whatever.
-I do have an 24x7 internet server, but do not guaranty 24x7
availibility or even sufficientbandwith.
-The recipients mainly use Outlook, some OE and some are Mac's.
 
 
Thx

 

Erwin Craps