I exchanged a couple of emails earlier this week with a very helpful lady called Melanie at SSC. They were already aware of a problem, and were working to address it. My newsletters resumed on Wednesday, but when I thanked Melanie for the resumption she did say that they hadn't actually fully sorted out the problem, so it is probably still being worked on.

Edit - by the way, I'm in the UK, so it doesn't appear the problem is restricted to any one region.