There are several things that might cause this. First check to see if you have any rules configured that might be moving these items to the deleted items folder. With Outlook open, click on Tools >
Rules and Alerts and if you find any rules created, disable them and test. A second option is that you might have a junk or adult content mail filter set up that could be moving these to deleted items.
For more information on , please refer to Knowledge Base article
195398.KB.EN-US
OL2000: How to Filter Junk and Adult Content E-mail