Send Broadcast Messages to All Users

Article
07/03/2012

Applies to: Office 365 for enterprises, Live@edu

Leaders in organizations often have to send e-mail messages to a large group of users. For example, you may have to send a broadcast message about a security incident or severe weather conditions to your users.

In the cloud-based service, the best way to do this is to set up a dynamic distribution group that lets you send a message to lots of users at one time. Membership for dynamic distribution groups is based on conditions that you define when you create the group. This means that the membership list for a dynamic distribution group is calculated every time a message is sent to the group.

As a result, new users created after you set up the group will receive messages sent to the group without any additional work by you. This makes the membership of dynamic distribution group much easier to maintain than distribution groups, also called "public groups", which require you to manually add members.

Create a dynamic distribution group to send e-mail to all students at your school

Let's walk through an example of how you can use dynamic distribution groups for emergency messages. You're the messaging administrator at Contoso University. During a recent winter storm, the school administration asked you to send e-mail to all students explaining which classes were cancelled and which facilities and services were closed because of the storm.

You sent the message to all the distribution groups maintained by individual departments. However, because membership of distribution groups is static, you weren't sure if the membership of these groups was up to date or if all students actually received your message. Your suspicions were confirmed when you heard reports that some students came all the way to school only to discover that classes were canceled and buildings were locked.

To prepare for next time, you decide to set up a school-wide dynamic distribution group, called "All Students" to help ensure that every student receives these important messages. You're convinced this is the best solution because:

Membership is dynamic, which simplifies maintenance.
Group members aren't displayed in the shared address book so you can maintain student privacy.
Messages sent to a group won't exceed the maximum recipient limits because groups are considered a single recipient.

Plan and prepare

Dynamic distribution groups use mailbox properties to determine membership, so you have to decide what mailbox property or properties to use as the criteria for group membership. You also have to decide who can send messages to this group.

Based on your research of dynamic distribution groups and your planning, you decide the following:

Use the CustomAttribute1 property to filter for membership. Because your hosted organization only contains mailboxes for students, you assign the value Student to this property. Faculty and staff mailboxes are located in your on-premises message system, and you don't yet provide the cloud-based service to alumni.
Assign yourself and the Dean of Students as the only people who can send messages to this group.

Set up a dynamic distribution group

With your plan of action in hand, you're ready to implement this solution by performing these tasks:

Configure the CustomAttribute1 property for all accounts.
Create the new All Students dynamic distribution group.
Specify who can send e-mail messages to the All Students group.

1. Configure CustomAttribute1

Because your hosted organization only contains mailboxes for students, run the following Windows PowerShell command to populate CustomAttribute1 with the value Student for all user accounts:

Get-Mailbox | Set-Mailbox -CustomAttribute1 Student

2. Create the All Students dynamic distribution group

With CustomAttribute1 configured with the value Student, run the following command to create the new dynamic distribution group using this attribute as criteria for group membership:

New-DynamicDistributionGroup -Name "All Students" -IncludedRecipients MailboxUsers -ConditionalCustomAttribute1 Student

The e-mail address for this group is allstudents@contoso.edu. The group appears in the shared address book, but group membership isn't displayed.

3. Specify who can send e-mail messages to the All Students group

By default, anyone can send message to a dynamic distribution group. So it's important to restrict who can send messages to this group. To configure the All Students group so that only you and the Dean of Students can send messages to the group, run the following command:

Set-DynamicDistributionGroup "All Students" -AcceptMessagesOnlyFromSendersOrMembers administrator@contoso.edu,student-dean@contoso.edu

Although the All Students group appears in the shared address book and anyone can address and send a message to this group, no one will receive a message sent to this group by anyone but you and the Dean of Students, and other senders will receive a non-delivery report (NDR) saying the delivery of their message failed.

Best practices

Consider these best practices when you set up and use dynamic distribution groups:

**Add the CustomAttributeN property when you first provision users **To do this, add a CustomAttributeN property to the header in the CSV Import file you use to provision users. This will save you from having to go back and configure a property after user accounts are created, like we had to do in our example.
**Use the CustomAttributeN property to segment your user population **A more real-world scenario may be to have students, faculty and staff, and alumni all hosted in a cloud-based organization. In this case, you could use the following values for the CustomAttributeN property for different kinds of users:
- Student
- FacultyStaff
- Alumni
This approach lets you segment your user population for future uses, such as using dynamic distribution groups to send tax information to faculty and staff or to send a fundraising letter to alumni.
**Use existing properties to help segment your user population **If you've already provisioned users in the cloud-based service, you may be able to use an existing property as the criteria for a dynamic distribution group. For example, you can use attributes such as Office, Department, or Title.
You can also use an existing property to help you configure the CustomAttributeN property. In our example, we assumed that the only cloud-based mailboxes were for students. But let's imagine that you also had cloud-based mailboxes for faculty and staff. When you provision faculty and staff mailboxes, you use the Office attribute for the room numbers. In that case, you could use the following command to add the value FacultyStaff to the CustomAttribute1 property:
```
Get-Mailbox -Filter {Office -ne $null} | Set-Mailbox -CustomAttribute1 FacultyStaff
```
So, for all mailboxes where the Office attribute isn't blank, we added the value FacultyStaff to the CustomAttribute1 property. This excludes student and alumni mailboxes because they don't have an office on campus.
**Use distribution groups that have closed memberships to limit who can send messages to large dynamic distribution groups **In our example, you and the Dean of Students are the only people who can send e-mail to the All Students group. This would be risky if either of you were unavailable to send an important or time-critical message.
A better approach would be to identify who may send messages to the All Students group and then create a distribution group, with closed membership, and add these people as members. Use the AcceptMessagesOnlyFromSendersOrMembers parameter on the Set-DynamicDistributionGroup cmdlet to enable the members of this group to send messages to the All Students group.
**Hide large dynamic distribution groups from the shared address book **You can restrict who can send e-mail messages to a dynamic distribution group, but you also might want to consider hiding these kinds of administrative-related groups from the shared address book altogether.
To hide the All Students group, using our example, run the following command:
```
Set-DynamicDistributionGroup "All Students" -HiddenFromAddressListsEnabled $true
```

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