Adding users to DL.

Question

I have a requirement to create a distribution list (DL) with external users and send email to that DL. Let’s say my domain is contoso.com.

Guest accounts already exist in Azure AD for these external users. My plan is to create a DL and add those guest accounts as members. If I add the guest accounts to the DL, will the external users receive emails sent to the DL?

If I add the guest accounts to a CSV file and run the following command, will the users user1(at)somedomain.com and user2(at)somedomain.com receive emails sent to the DL? (I have around 300 guest users.)

Import-CSV C:\temp\input.csv | ForEach-Object {     Add-DistributionGroupMember -Identity dl(at)contoso.com -Member $_.Users -BypassSecurityGroupManagerCheck } 

Is this the correct approach, or is there a better way to handle external users on a DL?

Answer 1

Hi Rising Flight

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

To answer your primary question directly: Yes, your approach is entirely correct and will work exactly as you intend. When you send an email to the distribution list, the external users (ex: ******@somedomain.com) will receive the email in their native inbox. Since your guest accounts already exist, your plan is the most direct and efficient method.

When you add an Azure AD guest account to an Exchange Online distribution list, the system is designed to deliver email to their actual external email address.

• The guest account's identifier in your tenant (ex: user1_somedomain.com#EXT#@contoso.onmicrosoft.com) is its User Principal Name (UPN), used for identity and access management.
• However, for mail delivery, Exchange Online uses the ExternalEmailAddress property associated with that guest account, which holds the real-world address (ex: ******@somedomain.com).

When an email is sent to your distribution list, Exchange Online expands the member list and correctly routes the message to the external email address for each guest member.

The PowerShell command you provided is the correct method for adding members to a distribution list from a CSV file. For the script to execute successfully, please ensure your CSV file is formatted correctly. The file C:\temp\input.csv must contain a header named Users, and each subsequent row should list the identity of the guest user. I recommend using the guest's UPN for reliability.

Example input.csv format:

Users

user1_somedomain.com#EXT#@contoso.onmicrosoft.com

user2_somedomain.com#EXT#@contoso.onmicrosoft.com

guest3_anotherdomain.com#EXT#@contoso.onmicrosoft.com

 Your command will then work perfectly:

Import-CSV C:\temp\input.csv | ForEach-Object { Add-DistributionGroupMember -Identity ******@contoso.com -Member $_.Users -BypassSecurityGroupManagerCheck }

While your method is the most direct for your current situation, it is helpful to be aware of other standard practices for handling external recipients.

• Mail Contacts: If the only purpose for an external user's identity is to receive emails (and they do not need to access internal resources like SharePoint or Teams), creating them as a Mail Contact is a more lightweight solution. A Mail Contact is simply an entry in your address book that forwards to an external address, without any associated user account or permissions.
• Microsoft 365 Groups: For scenarios requiring more than just email distribution, a Microsoft 365 Group is the modern, recommended alternative. It provides a shared mailbox, calendar, and collaborative workspace. You can add external guests to a Microsoft 365 Group, and they will receive group emails in their personal inbox, provided the group is configured to send copies of conversations to members.

For additional referral information:
Recipients in Exchange Server | Microsoft Learn

Create and manage distribution groups in Exchange Online | Microsoft Learn

B2B guest user properties - Microsoft Entra External ID | Microsoft Learn

I hope these suggestions provide some helpful.

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