If you are developing an OfficeJS add-in for Outlook or Outlook Online (OWA) and your project requirements have a need to peek inside distribution lists, you might find that there are two kinds:

• Distribution Lists – these are Exchange groups, or mail enabled Active Directory groups. These are managed by the enterprise IT and contain a list of email addresses and/or other distributions lists.
• Contact Lists / Private Distribution Lists – these are personal lists created by the user that can contain similar objects.

For an Office Add-in, you must use the makeEwsRequestAsync() command to submit EWS to Exchange. And the specific command you will need to use is ExpandDL to get the members of a DL (or contact list). With regards to the first item in the list above, it is pretty straight forward. For the second item there is this blurb on the page:

Private distribution lists are located in the Contacts folder of a user’s mailbox. Private distribution lists do not have e-mail addresses so their store item identifiers are used in an ExpandDL request. Members of a private distribution list can be any mail-enabled user, contacts or distribution lists from Active Directory, or contacts or private distribution lists from a user’s Contacts folder.

The bold part is key. But where do you get this. When you request a to.getAsync() and receive “Bob’s Favorite People” as a recipient item what do you do with it?

The key is to call the EWS method ResolveNames. When you call this on “Bob’s Favorite People” you will get a return value with PrivateDL and an ItemID (the Exchange Store Item ID in the users Contact folder) that you will then send that ItemId to ExpandDL. Here is what the soap response would look like from ResolveNames:

You can then make your ExpandDL request like this:

The result will be a list of all the email addresses, like this:

NOTE: For now the ResolveNames operation is not supported in my library easyEws. I am working to add it in the coming weeks.

Please let me know if you have any suggestions or questions.

NOTE: I am not an Exchange Web Services (EWS) expert, but have some experience with it through the OfficeJS makeEwsRequestAsync() command. To get the answer for this blog entry, I had to go to a real EWS expert to figure this one out. Many thanks to Dan Bagley (EwsEditor) for his assistance.