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How to Fix Guest Users Not Receiving Emails from a Mail-Enabled Security Group
Question details
Guest users are able to receive direct emails but do not receive messages that are sent to a mail-enabled security group they are part of.
- Product
- Microsoft 365 Exchange Online
- Device & OS
- not provided
- Scenario
- An administrator is attempting to send communications to a mail-enabled security group, but external guest users within that group fail to receive the messages.
- Observed behavior
- Emails sent directly to the guest user's address are delivered successfully, but emails routed through the mail-enabled security group fail to reach the guest user.
Ensure you have global administrator or Exchange administrator privileges in Microsoft 365 before attempting to run message traces or modify the directory's contact lists.
Remove Duplicate External Contacts
Identify and delete duplicate external contacts that share the exact same email address as the guest user to resolve mail flow conflicts.
In Microsoft 365, contacts are used to identify external users in Outlook. When an external contact and a guest user share the exact same email address, Exchange Online can encounter routing conflicts, causing group emails to drop. Removing the duplicate external contact typically resolves this issue.
Log in to the Microsoft 365 admin center using your administrator credentials.
Navigate to 'Users' and select 'Contacts'. Click on 'Export Contacts' to save a backup CSV file of your current contact list.
Search the contacts list for any external contact that has an identical email address to your affected guest user.
Delete the identified duplicate contact. Wait a few minutes for the changes to sync, then send a test email to the mail-enabled security group to verify delivery.
Run a Message Trace in Exchange Admin Center
Use the message trace tool to diagnose where the group email is being dropped or delayed.
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Frequently Asked Questions
Why do guest users receive direct emails but not group emails?
This usually happens due to a routing conflict in Exchange Online. It is often caused by having a duplicate external contact in the directory with the exact same email address as the guest user account, which confuses the mail flow when sending to a group.
How can I check if a group email was actually delivered to a guest user?
You can use the Message Trace feature located in the Exchange admin center under 'Mail flow'. By tracing the message sent to the security group, you can see the delivery status for each individual recipient, including guest users.
Is it safe to delete duplicate contacts in Microsoft 365?
Yes, provided they are genuine duplicates causing conflicts with your guest accounts. To ensure safety, you should always navigate to Users > Contacts in the admin center and export a CSV backup before deleting any contact entries.
What should I do if removing the duplicate contact doesn't fix the mail flow issue?
If emails still fail to reach guest users after removing duplicate contacts and waiting for directory synchronization, there may be deeper mail flow or forwarding configuration issues. You should contact Microsoft 365 technical support, as administrative backend access may be required to resolve the problem.
