Search Folder or Conditional Formatting for internal company emails

I’m looking for a way to more easily recognize internal mail, i.e. mail coming from our domain.

I’ve been successful to do this for several external domains via Conditional Formatting (as described in Highlight mail from a specific domain) but when I try this for our own domain, it doesn’t work.

Is there a way to achieve this either via Conditional Formatting or a Search Folder for our internal mail as well?

Internal Emails buttonThe reason why the described method doesn’t work for internal mail is because Exchange doesn’t use regular SMTP addresses (with the @ character) for internal mail but X.500 addresses which have a completely different format.

By using another searching value, you can still easily filter out or highlight internal email.

Search or filter value for Exchange emails

From buttonTo find all internally sent Exchange emails, you can do a search or apply a filter based on the From field. The value that needs to be searched for is; /O=

The /O= stands for the beginning of any X.500 address that is being used internally by Exchange to address people that are part of that Exchange organization.

The From filter value /O= allow you to find internally sent Exchange emails.
The From filter value /O= allow you to find internally sent Exchange emails.

Note: To see this value for yourself, you can apply a custom form and make the actual From email address visible as a column as explained in; Show sender’s e-mail address as a column in message view.

Creating the Conditional Formatting rule or Search Folder

Filter buttonWhen creating the Conditional Formatting rule or Search Folder to highlight or only show internal emails, it is best to search for the /O= value and your company’s email domain name (

This is to make sure that internal emails that are sent by different means (like a copier with a “scan to email” functionality or an automated system) are still included as these usually send out with the SMTP address in the From field.

  1. Open the “Condition…” or “Criteria…” dialog from the Conditional Formatting dialog or Search Folder.
    • Conditional Formatting
      • Simplified Ribbon (Microsoft 365)
        View-> Current View-> View Settings-> Conditional Formatting…
      • Classic Ribbon
        View-> View Settings-> Conditional Formatting…
    • Search Folder
      • Right click on Search Folders in the Folder Pane-> New Search Folder
      • Classic Ribbon
        Folder-> New Search Folder

    Conditional Formatting - Internal mail 
    When using Conditional Formatting, add a new rule with a unique color.

    Search Folder - Internal Mail
    When using a Search Folder, use "Create a custom Search Folder."

  2. On the Messages tab, type the following in the From… field (of course with your own company email domain);
    • /O=;

    Search for both /O= and to find all internally sent emails. 
    Search for both /O= and to find all internally sent emails.

  3. Press OK to close the Filter or Search Folder Criteria dialog.
  4. When you are creating a Conditional Formatting rule, click on the Font… button to select a unique color, font, font style and/or size.
  5. Press OK until you have closed all remaining open dialogs and are returned to the main Outlook window.

All internal emails from your company should now be displayed (Search Folder) or formatted with your font settings (Conditional Formatting).

Note: If your company is using more than 1 domain or is using a subdomain as well, then you can add these to the From field separated by a semi-colon like this; /O=;;;

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