SendGuard 365
In the SendGuard M365 settings, there is an option to check whether a distribution list contains external members. This setting is set as No by default, which means all distribution lists are treated as external unless configured otherwise. When set to Yes, SendGuard will analyze the list members and flag the distribution list as external if any external addresses are detected; otherwise, it will be treated as internal.
Please note that enabling this option may affect performance, as it requires retrieving detailed member information.
Below is the setting that enables this check:
*Ensure your Administrator grants the additional permission for the app using the option on the right.
To view the full list of recipients in the distribution list, select the Auto Expand option. This will expand all members, including those within nested distribution lists.
SendGuard COM Add-in
SendGuard’s COM Add-in includes a feature to identify external members within distribution lists. This functionality is controlled by a registry key named SCCheckDLMemberIsExternal.
When set to True: SendConfirm will inspect distribution list members. If any external addresses are detected, the list is flagged as external.
Default (False): SendConfirm does not check inside distribution lists. All lists are automatically treated as external and displayed as "xxx@distributionlist" in the SendConfirm prompt.
Managing Settings via SendGuard Management Console
Open the SendGuard Management Console.
Navigate to COM Add-in Settings > Advanced Settings.
Click Configure Registry Settings.
Find Check DDL Member External (SCCheckDLMemberIsExternal).
Select True to enable external member checking, then click OK.
Click Save to apply the changes.
Managing own Settings via Classic Outlook
Close Classic Outlook.
Open the Registry Editor (regedit).
Navigate to the following registry path:
Computer\HKEY_CURRENT_USER\SOFTWARE\VB and VBA Program Settings\addins4office\SendGuard\v5
Locate the key named SCCheckDLMemberIsExternal.
Set its value to True.