We like the envelope integrated into the lettering in #2 & #3, that's a great idea. We don't like the colors or font, so maybe play around with that a bit. #4 was a bit too plain for us.
Bens -- we really like the idea of the envelope in the "o" (especially #3) and would like to see some different renditions with a different font and different coloring. Are you interested in pursuing that or should we try to get other designers to play with that?
I've tried a coupleof different styles. I've just used grey and red for the time being. If you let me know which logo(s) you prefer, i'll show you a few colour options.