Extension Custom Attributes for Dynamic Distribution Lists in Office 365

I was browsing an online forum recently and saw someone with an issue creating dynamic distribution groups in Office 365. The mailing lists were based on the Office property. However, to accommodate users that work out of multiple locations the poster was trying to put a comma separated list in the Office property. Then for the distribution group the poster wanted to do a recipient filter including something like:

Office -like '*location1*'

This syntax works properly for on-premises Exchange but won't on Office 365. I assume that it is because Office 365 is trying to limit the load these queries place on the infrastructure.

In Office 365, you can't start your query with a wildcard. So, you can search for 'location*' but this only returns true if the value is at the start of the string.

The second bright idea I had was to fake it out and put a dummy value first. The I could use two wildcards to get the same effect. So, the query would be for 'X*location1*' but this didn't work either. There was no error for this one, but it never returned true. I suspect that the query is just tossed in the background.

Then I found out about some new attributes that were added starting with Exchange 2010 SP2 and are also in Exchange 2013/Office 365:

• ExtensionCustomAttribute1
• ExtensionCustomAttribute2
• ExtensionCustomAttribute3
• ExtensionCustomAttribute4
• ExtensionCustomAttribute5

These 5 attributes are not the same as the 15 CustomAttributes that have in Exchange Server for many versions. The CustomAttributeX properties are a single text string. The ExtensionCustomAttributeX properties are an array. This means that they can store multiple values that can be properly queried for a dynamic distribution group.

You can set multiple values for an extension custom attribute as follows:

Set-Mailbox Byron -ExtensionCustomAttribute1 London,Paris,Montreal

If you need to add or remove individual items to the attribute for a user, you can use the following syntax:

Set-Mailbox Byron -ExtensionCustomAttribute1 @{Add="Vancouver"; Remove "London"}

Creating the dynamic distribution list for recipients with Vancouver as an item in ExtensionCustomAttribute1 would be as follows:

New-DynamicDistributionGroup VancouverList -RecipientFilter {ExtensionCustomAttribute1 -eq "Vancouver"}

A final quirk about ExtensionCustomAttributeX and Dirsync. When you use Dirsync (Windows Azure Active Directory Synchronization), it will appear that ExtensionCustomAttributeX is syncing up to Office 365. However, it will never appear in the properties of the users. Somewhere in the background Windows Azure AD or Exchange Online discards the value. This is a known issue.

Monitor the following forum posts to see if there is any change:

• http://community.office365.com/en-us/f/613/t/89392.aspx
• http://community.office365.com/en-us/f/613/p/271828/831547.aspx