Many administrators don’t realize that Outlook by default has its own filtering in place. This filtering is very basic and it doesn’t usually cause any issues with your existing mail server security or 3rd party filtering. If you have exhausted your efforts in troubleshooting missing mail or false positives you may disable this filtering to see if that helps. To disable Outlook Filtering, follow these steps:
- Open Outlook
- Click Actions > Junk E-mail >Junk E-mail Options
- Select No automatic filtering;
- Press OK.