OK, here are the tips, tricks and traps so far...
- IMAP Migration is a little complicated. You can do this as an administrator but need the user to give you type their password in. It is setup in the administration windows
- Google Sheets don't work well in Safari. Seems to work fine in Chrome, but I can't seem to use the the menus, it gets stuck on "working". Not clear what is wrong, but have lots of ad blockers that I have. So it seems like Chrome is the choice, but I haven't tried Firefox.
- Routing. This is complicated. The important thing is to make sure that routing includes both recognized and unrecognized addresses. The default seems to be unrecognized and then it doesn't work.