Hi all - I've got a first pass at this email ready to test on cdev. Some of the links might not be 100% accurate, but this should be enough for us to gauge design.
I've attached a few screenshots to show you behavior across a couple different platforms and scenarios. Note that, in particular, email clients can't reliably load custom fonts. We are also using a fixed table width across devices because there's not reliable support for media queries across clients. IMO this looks pretty readable on narrow screens, but it would be helpful for Sara to take a look.
There are still lots of parts of the email flow that have to be looked at. One that jumps out for me, which is closely linked to this ticket, is that two emails are in fact sent on activation: the 'Welcome' email described here, and one from WPMU called "New CUNY Academic Commons User". I was going to disable the latter, but then I thought it might be worth reconsidering, since it includes information about the chosen username. Do we want to keep both? Or should we fold that information into the other email somehow?