This one is well hidden within Umbraco for some reason and is not adjustable with Contour from what I can see.
If you want your emails to show as something other than firstname.lastname@example.org then you will need to go into config/umbracoSettings.config.
You should find this in that file around line 30.
<notifications> <email>email@example.com</email> </notifications>
Change it to firstname.lastname@example.org or whatever you want/need it to be.