It has been a while since I could easily get the header of a received email, crtl+f for "received" and easily sniff the IP address of the sender. Alas, services such as Google (gmail) have updated their security measures so that such things can't be done anymore.
However, I read an OTW's comment to someone stating that the information is there, it is simply hidden. I tried to search for it but didn't found reliable info. Thus, does anyone have any info on this? Is it still possible to do this when the sender uses gmail for instance? Thx in advance.