Outlook moving Emails to Spam despite delivery to inbox on server

If your email server (like Exim on a cPanel server) is delivering a message to the INBOX, but Outlook is still showing it in the Spam or Junk Email folder, the cause is almost always client-side filtering in Outlook itself. Here’s how to fix this reliably.

Problem

Emails from @senderdomain.com are being delivered correctly to INBOX by the server, but IMAP linked Microsoft Outlook automatically moves them to the .spam or Junk Email folder.

Why This Happens

Outlook has a built-in Junk Email filter that scans incoming email messages after they are downloaded via IMAP. Even if Exim or Dovecot delivers to INBOX, Microsoft Outlook may override that based on its own assessment. Any changes to an email's location or classification made by Microsoft Outlook is synced to the server via IMAP and then synced to all your other devices connected via IMAP to the email account.

“Outlook moves suspected spam to the Junk Email folder even when using IMAP.”
– Microsoft Support

🔧 Step-by-Step Fix

1. Add Domain to Safe Senders

1. Open Outlook and go to Home > Junk > Junk Email Options.
2. Go to the Safe Senders tab.
3. Click Add, then enter: @senderdomain.com
4. Check “Also trust email from my Contacts” and click OK.

2. Add Specific Email or Domain

3. Access Junk Email Settings

4. Mark Past Emails as “Not Junk”

• Go to the Junk/Spam folder.
• Right-click the email from @senderdomain.com.
• Select Junk > Not Junk and confirm you want to add it to Safe Senders.

5. (Optional) Check Antivirus Plugins

Some antivirus tools (e.g., BitDefender, Norton, McAfee) have their own spam filters. Either disable them or whitelist the domain in their email filtering settings.

🛡 Server-Side Best Practice (Optional)

• Whitelist @senderdomain.com in cPanel’s Spam Filters settings.
• This ensures SpamAssassin won't score it as spam or add misleading headers.

📌 Summary

• Server is delivering email correctly.
• Outlook's junk filter is responsible for moving it to spam.
• Add sender to Safe Senders list and disable automatic filtering.

Note: Some of the above options name, layout may in Outlook depending on the version install and the operating system in use. However the basic underlying functionality is the same