content disappearing from emails rec'd

Occasionally, and not from any particular user, I will receive an email, and
the alert for that email with the preview of what the email says will pop up
in my lower right hand corner. But when I go to the email in Outlook, the
response portion is empty.

They are all responses to various emails I've sent, and that content is
there, however the response the person sent to me is not. But again, there's
something when it sends me the alert.

Any ideas?