AND it could create a dis-incentive to load up an email with unique images since as soon as you send the email out all of those gmail addresses are coming right back at your server to request the images.
You can somewhat do this with the current system. I had no problems sending an email with 10 10mb images. Google happily fetched all 10 of the images off my server.
Not sure if they limit it at some point, but if a server accepts urls such as:
Google would fetch each separately. Send this out to a bunch of people, and it seems problematic. I'm going to be optimistic, and assume they built in some sort of limiting, but who knows.
We manage opt-in mailing lists for customers of restaurant chains, and for well timed, well-targeted campaigns they get open rates in the 30%-40% range with the majority of opens within 15-30 minutes of the send anyway. It takes more resources for us to handle the outbound mail load than to handle the inbound image requests, as for the image requests the url's contains enough info to do a trivial regexp based rewrite and fetch the images from a cache. I don't think handling a 100% open rate as soon as the mail was delivered would even remotely be a challenge.
