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I wouldn't mind the 1.5 MB. It is only one week after all.
I would prefer the weekly e-mail - with headlines, catch-lines, and a direct link to the article. I don't think a text e-mail will be very big. I just copied the last seven days' worth of headlines and catch-lines into a text editor, and it was only 20KB - with links and some frilly additions and any encodings, that should only come out to 50KB at the most. Plus, it's the same, or even less load than sending seven daily e-mails (you could schedule the weekly e-mails to send out on different days to share the load out across the week). If you are really worried out bandwidth, headlines-only would work I guess, but might cause additional load on the servers because of users having less information for people to decide which articles they are interested in.