Office 365: Allow External Senders to Email a Distribution List
A distribution list, also known as a distribution group, is a collection of email addresses treated as a single recipient. It simplifies sending emails to groups of people within an organization. As an Office 365 administrator, you may want to allow people external to your organization to send emails to a distribution group. By default, external senders are blocked from emailing distribution lists for security reasons. However, there are ways to safely allow these external emails so you, your users, and your partners can collaborate efficiently.
Enabling external senders to email a distribution list in Office 365 is a straightforward process. To allow external senders to email a distribution group, you can perform the necessary configurations in the Microsoft 365 Admin Center, Exchange Admin Center, or Exchange Online PowerShell. In this beginner’s guide, I’ll explain step-by-step how to enable emails from external senders to Office 365 distribution lists.
Key Takeaways:
- Enabling external senders enhances collaboration and communication in Office 365.
- By default, distribution groups do not accept emails from external senders.
- Error code 550 5.7.133 is commonly associated with non-delivery reports (NDRs) for external senders trying to email a distribution group.
- Configuration changes can be made through the Microsoft 365 Admin Center, Exchange Admin Center, or PowerShell.
- Before opening up distribution group emails to external senders, make sure You Use Office 365 Advanced Threat Protection to scan all emails and attachments for malware and phishing attempts.
- If possible, control external access only to approved domains.
How to Allow External Users to Email a Distribution List?
By default, distribution groups do not accept emails from external senders. This can result in non-delivery reports (NDRs) with error code 550 5.7.133. While distribution lists are useful for internal communication, businesses sometimes also need to share information or updates with external partners. This might include vendors, contractors, or customers, among others. By default, however, Office 365 restricts external senders from accessing distribution lists. So how can you enable external senders to a distribution list in Office 365?
To allow external users to email a distribution list in Office 365, you need to modify the distribution list’s settings to accept messages from outside your organization. Here’s how you can do it:
- Log into Microsoft 365 Admin Center: Use your administrator credentials to sign in to the Microsoft 365 Admin Center.
- Access the Groups Section: In the Admin Center, expand the “Teams & groups” in the left navigation and click on the “Active Teams & groups” section.
- Select the Distribution List: Find the distribution list you want to modify from the list of groups and select it. Click on the distribution list to open its properties.
- Allow Emails from External Senders: Within the group settings, Under “General settings,” enable “Allow external senders to email this group.”
- Save Changes: After making the necessary changes, make sure to save them. This will apply the new settings to the distribution list.
These steps will enable the distribution list to receive emails from external users. Alternatively, you can also achieve this by navigating to the Exchange admin center (EAC).
Exchange Admin Center: Allow External Senders to Email a Distribution Group
To allow external senders to send emails to a distribution list in Office 365, you can adjust the message delivery restrictions for the distribution list. Follow these steps:
- Access the Office 365 Admin Center: Log in to the Office 365 Admin Center using your administrator credentials. You can access it by visiting https://admin.microsoft.com and entering your credentials.
- Navigate to the Exchange Admin Center: In the Admin Center, locate the “Admin Centers” option and click on it. From the drop-down menu, select “Exchange” or “Exchange Admin Center” to open the Exchange admin interface.
- Find the Distribution List: In the Exchange Admin Center, expand the “Recipients” tab. Click on “Groups” to access the group management settings.
- Select the Distribution List: Locate the distribution list you want to allow external senders. Click on the name of the distribution list to open its properties.
- Adjust Message Delivery Restrictions: In the properties of the distribution list, click on the “Settings” tab and click on the “Edit Delivery Management” link. Change the setting to “Allow messages from people inside and outside my organization” to allow external senders to send emails to the distribution list.
- Save Changes: Once you’ve adjusted the message delivery restrictions, save the changes by clicking on the “Save Changes” button.
By following these steps, you can allow external senders to send emails to a distribution list in Office 365. This ensures that users outside your organization can successfully communicate with the distribution list. Refer to Microsoft documentation at: https://learn.microsoft.com/en-us/exchange/recipients-in-exchange-online/manage-distribution-groups/manage-distribution-groups
PowerShell to allow external users to email a distribution group in Office 365
When it comes to configuring distribution groups in Exchange Online, you have two options: the Exchange Admin Center and Exchange Online PowerShell. The Exchange Admin Center provides a user-friendly interface for managing distribution list groups. You can easily add new groups, view and modify group properties, and adjust various settings. On the other hand, if you prefer a command-line interface, Exchange Online PowerShell allows you to automate and script group configurations. Both options offer flexibility and control, so choose the method that aligns with your preferences and requirements.
Here is the PowerShell script to allow external users to email a distribution group:
#Parameters
$DistributionGroupID = "ProductionManagers@Crescent.com"
$AdminAccount = "Salaudeen@Crescent.com"
# Connect to Exchange Online
Connect-ExchangeOnline -UserPrincipalName $AdminAccount
#Get the Distribution List by its Email
$DistributionGroup = Get-DistributionGroup -Identity $DistributionGroupID
If($DistributionGroup -eq $null)
{
Write-host "Couldn't find the Distribution List '$DistributionGroupID'" -f Red
Exit
}
# Set the "Allow external senders to email this group"
$DistributionGroup | Set-DistributionGroup -RequireSenderAuthenticationEnabled $false
This will allow external senders who are not authenticated to send messages to the distribution list.
Conclusion
 By following these simple steps, you can allow external senders to send Emails to your Office 365 distribution lists. This can be a useful feature for businesses that work with external partners or clients, as it allows them to communicate more easily and efficiently. As always, it’s important to be mindful of security and to ensure that you’re only allowing access to trusted external senders.
It is also essential to confirm that the external mail flow is functioning correctly. Track messages sent to the distribution group and monitor any NDRs or delivery failures. Lastly, allowing external senders to email Office 365 distribution groups opens up communication for impactful collaborations while introducing risk. Apply the security best practices to enable the business value while preventing phishing attacks and malware. Continue monitoring external sender allowances over time, ensuring partner access aligns with organizational needs.