I did not get an email from Apple but when I checked Apple's site, the projected arrival date always agreed with whatever arrival date UPS was showing, except when UPS went "dark" during customs clearance. Then the UPS site would say "delivery date not available" but Apple would still show whatever they were showing before. Once my phone got through customs, both UPS and Apple started showing updated information.
I ordered a Space Grey 64 GB model on the morning of 10/27 and was given a Dec 8-16 delivery window. A few weeks ago it improved to Dec 1-7. Then when I least expected it, my status went to "preparing for shipment" and my date improved from Dec 1-7 to Nov 24. My phone was in "delivery date unavailable" status on UPS web site for only about 1 business day then it showed Anchorage AK for almost a whole day with a delivery estimate of 11/21. The next thing I knew the delivery estimate improved to 11/20 and I went on ups.com to buy a guaranteed delivery window of 2-4pm so I wouldn't be stuck sitting at the house for 4 or more hours during my busy holiday preparations. The phone showed up at 2:20pm and I happily paid the $8 surcharge. An hour after it arrived, I had all my data on it and by 8pm that evening all my apps had downloaded and the only way I knew I was using a new phone was by looking at the notch at the top of the screen and the fact I could unlock it by looking at it.
I've said before in this thread that having delivery status change to unknown while in customs is disconcerting but I would imagine UPS does it for legal reasons. UPS doesn't want to be held accountable for missing a delivery date if US Customs decides to take an extra day or two inspecting a pallet of iPhones. I don't like it but I don't blame UPS one bit.