Solution for How to Delete IMAP Outlook Email that Won't Go Away [Random]

If your emails in Outlook are gray out and strike-through, but won't go away, do a purge. 

I couldn't figure out how to get rid of these entries for a very long time:

On a recent googling, I finally learned that I need to do a purge to get rid of it. I use IMAP to access my emails, and I suppose Outlook is cautious about deleting things. In Outlook 2007, the PURGE option is located under the EDIT menu. 

Reference: https://support.office.com/en-us/article/purge-imap-items-marked-for-deletion-ac1c51da-31c1-435c-a357-96eb78ad684a