how to fix AD to Entra Sync issues

Hi @HA 

Thank you for posting your question in the Microsoft Q&A forum. 

You’re seeing expected behavior in a hybrid Exchange environment. When you add a user to a Distribution List in on‑premises Active Directory, that group is synchronized to Microsoft Entra ID using Microsoft Entra Connect. Because the group is directory‑synchronized, Exchange Online treats it as read‑only, so membership cannot be changed in the Exchange Admin Center.

Microsoft Entra Connect synchronizes every 30 minutes by default, unless a custom schedule is configured. Any changes you make to the distribution group in your on‑premises Active Directory will only appear in Microsoft 365 after the next synchronization cycle.

If you need the change to appear immediately, you can manually trigger a sync. For details about how synchronization is scheduled, refer to Microsoft Entra Connect Sync: Scheduler - Microsoft Entra ID | Microsoft Learn 

I hope this helps clarify the behavior. 

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".   

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.  

To resolve the issue of a user not appearing in a distribution list in Microsoft Entra after being added in on-premises Active Directory (AD), you should ensure that the distribution list is properly synced. Here are some steps you can take:

1. Check Synchronization Status: Ensure that the Azure Active Directory Sync tool is functioning correctly and that there are no sync errors. You can use the Microsoft Entra Connect Health for sync to monitor the synchronization status.
2. Verify Group Type: Make sure that the distribution list is a mail-enabled security group, as only these types of groups can be synced to Microsoft Entra.
3. Use IdFix Tool: Run the IdFix DirSync Error Remediation Tool to check for duplicates, missing attributes, or rule violations that might prevent the user from being added to the distribution list.
4. Manual Updates: If necessary, manually update the user attributes in on-premises AD to ensure they are correct and then trigger a sync.
5. Wait for Sync: After making changes in on-premises AD, it may take some time for the changes to reflect in Microsoft Entra. Ensure that you allow sufficient time for the synchronization process to complete.
6. Check Permissions: Ensure that you have the necessary permissions in both on-premises AD and Microsoft Entra to make changes to the distribution list.

If the problem persists, further investigation into the specific sync errors may be required, and reviewing the logs from the Azure AD Connect tool can provide additional insights.