Approval mail stuck in mailbox inbox

I know this question may not be an oracle issue but it is related. So we have purchasing and journal entry that is going through workflow approval. When it is working fine, the user can either approve the po, req or je by login to the application and find it in the worklist and approve, or they can approve from their email within outlook. Sometime we get issue with the mailbox, where the approval emails will stuck in the inbox and not getting processed and move to the process folder of the workflow email box. When this happens, we usually