Outlook Limitations
Once you send your emails out to your clients and contacts they are typically no longer in your control. This is because if you send from the desktop version of Outlook you can disable the Forward button but as soon as the email goes out of Outlook, or you receive an external email, you can’t disable it.
Copy and Paste
And of course, if somebody really wanted to forward your content, they could just copy the content and paste it into a new email.
Very Sensitive Content?
If your content is very sensitive you do have some options to secure it. You could create the content in Vuture landing pages and then secure it by IP, secure site or double opt-in. The email sent to your client contains a link to this sensitive content and you can choose if you want to oblige your client to log in with a password (secure site) or be emailed a new link (double opt-in).
Secure by IP
If you don’t want to oblige your clients and contacts to click through and access a new link then another solution would be to save the content as an image in Vuture then secure the image by IP address. Clients would be able to view the content in the email but only if they are connected to their office network. There is a description of how this works on the Help Desk here.