Since posting i've realised I'd misunderstood some terminology - I'd assumed 'mouse enter' meant clicking on a button (like using the enter key); I've now discovered it means moving the pointer over the button, so no wonder an email opened when the cursor moved over the button. It's 'mouse down' that means a click (http://tinyurl.com/bw9lqpz).
To set up a 'submit by email' function in acrobat 9 it's necessary to create the button, then set it up to 'Submit a form' NOT to 'Attach to Email' (even though that's what happens...go figure!?) then in the next dialogue box specify the 'mailto:....' address. it's also necessary to 'Extend features in Adobe Reader..' so that reader can save it before attaching to an email.
The 1st time you use the Email button in reader, a pop-up dialogue appears asking whether you use internet mail or system based (e.g. hotmail or outlook), if system based is chosen then a blank email opens with the pdf attached.
I still don't understand what's going on with the email function in Adobe LiveCycle. Actually, I'm not clear what the difference is between LiveCycle & Acrobat - I'm very new to this area & am learning by trial & error.....everything's done on a wing & a prayer (with a few curses thrown in too!)
Cheers anyway guys