When mail vanishes.
WHAT TO CHECK FIRST
Webmail. That shows what is actually on the server.
IF IT IS THERE
A client problem: synchronisation, filtering, or folder configuration.
IF IT IS NOT THERE
It was deleted, moved, filtered, or never arrived.
THE POP CAUSE
A device configured as POP downloaded and removed it.
Check every device.
THE FILTER CAUSE
A filter moving mail to a folder, or deleting it.
Check your filters in cPanel and in your client.
THE CLIENT RULE CAUSE
Rules configured in the client, separate from server filters.
Check both.
THE COMPROMISE CAUSE
A rule you did not create, hiding or deleting mail.
That indicates a compromised account. Change the password immediately.
WHAT ELSE
Mail in Spam or Trash Mail archived rather than deleted
WHAT TO DO
Search webmail, including all folders.
WHAT TO ASK US
If it is genuinely absent, open a ticket with the sender, recipient and approximate time.