[icebraining]

The problem with attachments is that you increase the bandwidth on the sender. So, instead of, say, the sender spending 2k bandwidth per mail and each recpient another 60k on bandwidth to get images when opened, the sender pays for all that extra imagery bytes.

But wouldn't the sender have to serve the images over HTTP anyway? Unless you expect a big percentage of those emails to never be opened, but then I have to wonder if you should be sending them in the first place.

[mwexler]

Yeah, not everyone opens the mail, so the recipient shouldn't have to deal with the larger download (and the sender doesn't have to send a larger mail), and also, the opens are more distributed over time (for the most part, depending on when you send and to whom), so you can send the smaller mails faster but have a more even distribution of bandwidth as the opens occur across a longer period.