Exchange Online/Office 365 does not have dynamic distribution groups. So, in a hybrid deployment, it's not possible to synchronize dynamic distribution groups from on-premises to Office 365. There are two work arounds:
If you like scripting, you can create a script that updates the membership of a normal distribution group. You'll need to run the script as a scheduled task. The main benefit to this method is that it is contained entirely within the on-premises environment.
There are two drawbacks to this method:
- It's not actually dynamic, so there is a lag time from when new members are created and when they're added to the group.
- It's relatively complex to create the script and schedule a powershell script to run as a task with the correct snap-ins loaded.
My preferred option for this is to create a contact in Office 365 that points at the dynamic distribution group on-premises. This allows you to continue using true dynamic distribution groups on your on-premises environment and give Office 365 users the ability to send messages to them.
When you create the dynamic distribution group you need to select the following recipient types:
- Users with Exchange Mailboxes. These are your on premises users.
- Users with external e-mail addresses. These are your office 365 users.
- Display Name
- Email address (not the mail.onmicrosoft.com address)
- Display Name: same as dynamic distribution group
- Alias: same as dynamic distribution group
- External email address: same as email address from dynamic distribution group
You can't create the contact locally and sync it for two reasons:
- You can duplicate the same display name on two objects. So, you'll end up with two objects using the same display name. This will be confusing for on-premises users who will see both objects.
- You can't duplicate the external email address for a contact with the actual email address for the dynamic distribution group. This makes it not just a bad idea, but a technical impossibility.