Now it will seem to the sender that 100% of e-mails sent to Gmail recipients have been opened, rendering actual measurement impossible. A unique ID is useless if all unique IDs are requested all the time.
I'm sure they built-in rate-limiting to prevent DDOSing the sender's image server...
Apparently not. First, only messages read in gmail.com and Gmail mobile clients (not any other email clients). And apparently the image is not requested from the sender until the message is opened. Finally, apparently any querystring parameters will continue to function as usual.
I'm sure they built-in rate-limiting to prevent DDOSing the sender's image server...