Treat Distribution Lists as Internal
By default, SendGuard treats all distribution lists as external recipients.
If your distribution lists only contain internal recipients, you can configure SendGuard to treat those lists as internal. This prevents unnecessary external recipient warnings for these lists.
Important: When you add a distribution list as an internal domain, SendGuard will treat that entire list as internal. Ensure the list only contains internal recipients before adding it.
Configure Distribution Lists as Internal
Step 1: Open the SendGuard Management Console
Log in to the SendGuard Management Console.
Step 2: Open the SendGuard Settings
- Select Details.
- Select Edit M365 Settings.
Step 3: Add Distribution Lists to Internal Domains
- Under General Settings, locate Internal Domains.
- Add *@DistributionList to the list of internal domains.
*Note that this will mark ALL distribution lists as INTERNAL recipients.
- Click Save.
Step 4: Refresh SendGuard Settings
Any changes to settings may take up to 4 hours to apply. For immediate testing, click Refresh settings in Outlook (if available), or use Outlook Web App (OWA) in a private/incognito browser. After saving your changes, refresh your SendGuard settings to apply the update.
https://standss.smartertrack.com/kb/a337/why-are-my-new-sendguard-settings-not-showing-up-in-outlook-immediately.aspx
Troubleshooting
If SendGuard continues to display an external recipient warning:
- Confirm the distribution list email address was entered correctly.
- Ensure the list was added under Internal Domains.
- Refresh SendGuard settings after making changes.
- Confirm the distribution list does not contain external members.
Treat Distribution Lists as External
Despite the option to
check within distribution lists, we recommend that SendGuard does not check the
individual members of a distribution list when evaluating recipients. Checking
each list member can impact performance, especially for large distribution
lists or environments with slower network connections. However if you wish to
allow SendGuard to verify external recipients in exchange distribution lists,
here's how: How to Enable SendGuard to Verify External Recipients
in Exchange Distribution Lists? As a result, SendGuard
will display a send confirmation prompt whenever an email includes a
distribution list, even if all members of that list are internal users.