This one puzzles me...

My Outlook 2013 has seven POP3 email accounts set up with their own .pst folders. That works just fine for six of the accounts, but one. These are the folders where the two email accounts reside:

C:\Users\UID\Documents\Outlook Files\mailbox_01.pst
C:\Users\UID\Documents\Outlook Files\mailbox_07.pst
The numbers reflect the order the accounts had been created. As the matter of fact, mailbox_07.com had been created long after the first one.

The issue I have is that the email received by mailbox_07.com is copied, not moved into the mailbox_01.net. In another word, both POP3 email accounts have the mailbox_07.com emails showing up. The reverse is not true, emails received by the mailbox_01.net are not copied/routed to other email accounts. This impacts in and outside emails as well for some reason.

Outlook did have 6-8 email rules, but none for the mailbox_07.com. My initial reaction had been to delete all of the rules and restart Outlook, just in case. That didn't resolve the issue.

Short of delete/recreate mailbox_07.com account, is there anything else that would fix this issue?
TIA...