Due to architecture of Exchange servers the emails sent internally (within your organization) are not filtered for spam. If messages from internal senders end up in Junk folder it might be caused by the following local reasons:
- Outlook Junk Filtering. We do recommend to have it OFF, as it may move emails to Junk folder without any reason. In Outlook 2010/2013 navigate to Home > Junk > Junk E-mail Options > Options > set to No Automatic Filtering.
Outlook 2011: Home > Junk > Junk Email Protection > Level > set to None.
- Outlook Plugin. Check your active plugins in Outlook > File > Options > Add-ins > Go > uncheck any antivirus plugins user has there.
- Outlook Block List. Check whether your company's domain/sender email address is added to Blocked list in Outlook 2010/2013 > Home > Junk > Junk E-mail Options > Blocked Senders.
Outlook 2011: Home > Junk > Junk Email Protection > Blocked Senders (note: to remove entry from the list Junk filtering should be ON).
OWA: Options > See All Options > Block or Allow
- Outlook Rules. Check whether user has any rules in Outlook which may move emails to Junk. In Outlook > Home > Rules > Manage Rules and Alerts.
Outlook 2011: Home > Rules > Edit Rules > Exchange. OWA: Options > Organize email > Inbox Rules.
Note: if you use SMTP devices to send messages on behalf of your mailboxes (scanners, copiers, web-forms, etc...), those emails are not considered internal, and flow usual path through mail filters. One of the reasons why those emails may end up in Junk folder is failed SPF record validation. To prevent this from happening add device's IP address to SPF record.