Thanks for that Stephane...unfortunately the company situation is that all web mail sites are currently available.
I did hear that DLP is not a 'blocking' tool...
So here is a slightly alternate question, can a policy be created to search just for outgoing emails that include an attachment and 'block' on those?...if say for example a very wildcard set of criteria is included in the search for the contents of that attachment EG a,e,i,o,u or 1,2,3,4,5 etc?....