Hi,
In the Messages app > Preferences > General Section > AppleScript drop down use the Open Scripts Folder option.
Once there you can open the Speak Events one as this will be the closest starting point to what you want to do.
(my List includes some older ones I used in iChat)
In broad terms you need to Copy the Script so that you don't lose the Original.
Change the name of the Copy version.
Then it needs to be altered so that it calls the Mail App and sends the contents of the message to the Email address you want it to go to.
The Buddy List Status Messages that shows what is Playing in iTunes is also an AppleScript. (finding it is an issue) However it does tell you how one app can access another.
Asking further questions here may help Mac OS X Technologies
8:45 pm Monday; January 25, 2016
iMac 2.5Ghz i5 2011 (Mavericks 10.9)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad