I ask because a few weeks ago I sent a newsletter and it had about 14% open rate which is pretty typical right now for that subscriber list, then I sent the same email a couple of days ago and the open rate jumped to 34% which is unheard of for that group. Upon investigation all of the additional recipients were google email users so I'm wondering if maybe the google server caching of that one image was disabled for a period and so let all of the real opens count for that one email. I haven't seen numbers like that since.