IT

If you can find the settings for your mousepad you can adjust the "palm sensitivity" so that the cursor doesn't leap all over the place at a slight brush by your wrist (I have only just found this setting. "Palm" confused me for a while, as it is the heel of my hand that brushes the touchpad, not my palm)

ladybird I can't help you but I can sympathise because mine does it too periodically!
I think.......... it happens when the mouse pad arrow (as opposed to the 'blinking' cursor, isn't in the message box. It happens on here too, and if I then move the mouse arrow into the box, it stops!

I'm sorry if that's as clear as mud well, I know what I mean

Are you using a laptop to write your email as sometimes your wrist can accidently touch the mousepad. Depending where you mouse pointer is on the page it will either select an item or move the coursor.

Hope this helps

Does it look as if the cursor is gobbling up the words in front of where you are trying to type.
Could be possible that you have hit the 'insert' key. It's just to the right side of the large 'Return' button. Click this key marked insert and see if this helps. If this wasn't the cause ---- and it didn't correct the problem, it might start to gobble to keys in front, so just click it again to deactivate it.

Good luck