To resolve issues with emails disappearing after being read in Exchange, try these steps:

1. Check your mailbox settings to ensure that emails are not set to automatically delete after being read.
2. Verify the user's device settings; ensure the correct email account is logged in, and that no other apps are configured with the same account.
3. Check the mailbox folder configured to receive emails (e.g. Inbox, Spam, Archives).
4. Verify that the content of emails is not being sorted out due to pre-defined mailbox rules.
5. Check whether the emails are being filtered out by the server (e.g. Fraud Protection, or Anti-Malware).
6. If the user is not using the latest version of Exchange, it may be beneficial to update his version.