I have a client who has an online store, and receives order notifications by email.
Their order emails are flowing into their mailbox on the server, but never show up in Outlook.
Their Outlook is configured as POP, I have reset the mailbox password to ensure no other connections, there are no rules created. If I turn off POP auto-delete, I see the order notification email in the IMAP inbox, but (even with search) I cannot locate it in Outlook.
What else could it be/what else can I check?
Look at the server logs and see if there are other devices popping the account. It sounds to me there is another device (maybe a cellphone)/messing things up. The log file might also provide other clues
Alternatively change the password and see if the problem goes away. Also consider migrating from POP to IMAP on all your devices.