Thank you for taking the time to help me. I appreciate it.

I tried clicking on showing all messages, and it made no difference.
After spending an hour on the phone with Spectrum, our email provider, and then another hour on the phone with Microsoft, each said the problem was in the other one's program.

So I decided that I would try to make an end-run on it. I set a rule in Outlook that any message that comes into my inbox is immediately moved to a different file I set up called "Attention Needed." And it seems to be working. New mail shows up in the "Attention Needed" file and, importantly, it stays there. So now, I not only see the new mail as it comes, I also can look at and respond to yesterday's, last week's, and so on.

Your name says it all: whycantitbesimple Thanks again.