Option to not open mail titled "Retrieving data" or "..."
Sometimes when you just log in, or Reload UI from the mail window, the new mail shows as "Retrieving data" or "...". The Open All Mail button will still start dumping these items into your inventory but Accounting can't track them yet.
Yes, you should wait a few seconds, but this option would help offset human error when we get a little click happy.
This is an issue on Blizzard’s end. Mailing already tries a few times.