I think you should warn customers about the new fonts not working. I had been working on our monthly email that we send out, previewed it, and once it was emailed out it looked nothing like my preview. I was originally skeptical to use these new fonts because not everyone gets the same font, however, I thought if they were on constant contact then they have to work. Or else why would you have them?
Our monthly email now looks plain, incorrect, and nothing like the preview. Disappointing.
I would recommend not using these new fonts when sending out emails.