We need href display conventions for new windows and mailto

Situation 1 : You use a web mail client but you still have a desktop mail client installed. You click a mailto link because you think it's going to take you to a web contact form and it launches your desktop mail client.

Situation 2 : You click a link and it opens a new browser tab/window when you didn't expect it or you expected it would open a new browser window and it didn't so you lost your train on thought in the original page.

We need some conventions to stop this happening.