Blueberrybook for the emails maybe you could work on writing them out and saving the draft or walking away for 5-10 minutes, coming back re-reading and editing? I type fast so can really ramble myself if not careful. You could even wait to put the email address of the recipient in or write it in Word then copy and paste when ready to send to slow you down.

With overtalking, maybe you can practice your listening skills and actively taking a moment to ask the other person a question? Sometimes I find when I overtalk I haven't caught my breath to let the other person get a word in edgewise. I just noticed myself doing this with my SO on the phone. Then was like, oops, why don't you tell me what's going on with you? With some of my best friends it doesn't matter too much because we all talk a mile a minute when together and they can keep up. With others I need to make sure I slow down, though. Not sure if this idea would help or anything, but it's just a thought.