Can’t delete IMAP messages under Apple Mail and running Mavericks? Check out this tip.
If you are running Apple Mail under OS X 10.9 and have contracted with an ISP or mail service other than iCloud AND you’ve configured your email account as IMAP rather than POP, you may notice a peculiar system response, whereby you tell the software program to remove one or more messages located in the Trash folder and it fails to comply with your request. Instead, the message reappears in the Trash.
As seen in this YouTube video, one easy way to get around the problem (until Apple releases a software patch) is to delete the same messages a second time.