Try shift + F9 to rebuild your view index if your Lotus Notes emails mysteriously vanish.
I’m stuck with Lotus Notes as my email client at my day job, and one morning I found that a number of my Inbox messages (documents, in Notes parlance) had inexplicably disappeared. New mail was showing up fine, but some five thousand messages had simply vanished. I tried the usual common sense things, such as toggling the View All / View Unread options, checking the Trash, and restarting Notes, but all to no avail. I was stumped, and worried that my mail might have gone the way of the dodo.
Then, I got some great tech support from headquarters, and learned that the index for my views of the database were simply in need of a re-build. You can press Shift and F9 (at the same time) to rebuild a view index. After I did this, my messages magically reappeared.
(Thanks to Sonja Houze for her consummately professional assistance.)