Takes forever to delete messages in Outlook 2010

[mike13]

My wife reads most of her messages on her cell phone, and then deletes them there, but they are NOT deleted from her computer running Win 8.1 and Outlook 2010. She now has over 1,000 messages in her inbox that are not read. When we click on a message and then click the Delete X at the top of the screen, it takes at least 20 seconds to delete that message. Sometimes I notice this message at the bottom of the screen "UPDATING CACHED MESSAGES  0/1053  How can I delete 99 % of these messages a lot faster ?  Thanks, Mike

[mike13]

Update, well I slowly deleted one message after another. It finally got faster, and now she has about 20 to 30 messages in her INBOX.