How to enumerate Mail Folders with all child folders

Question

Currently, as far as I can tell, Microsoft graph offers 2 primary endpoints for outlook mail folders according to

https://learn.microsoft.com/en-us/graph/api/user-list-mailfolders?view=graph-rest-1.0&tabs=http

List mail folders and List child folders - meaning just to build the folder hierarchy in my app, I need to make recursive REST API calls - which is very slow and very bad.

Is there any way to get microsoft to just return all folders at once?

If it is not then how to make a recursion on child folders and it's sub folders.

Answer 1

Hi @Brown, Micah

You can use GET /me/mailFolders/{id}/childFolders to get a MailFolder and Sub Folders also in single API call.
For example: There is a subfolder present in my inbox, Using the below API we can get the SubFolder-id:

https://graph.microsoft.com/v1.0/me/mailFolders/inbox/childFolders  

After this use the SubFolder-id in the below API to get subfolders present in that Folder.

https://graph.microsoft.com/v1.0/me/mailFolders/{SubFolder-id}/childFolders  

Similarly you can traverse through all subfolders.

Further you can refer to these similar posts-

• Iterate through mailfolders
• List all folder and subfolder using microsoft graph

Hope this helps,

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Answer 2

The beta endpoint will return all folders (eg it does a deep traversal) https://graph.microsoft.com/beta/me/mailfolders?$select=displayName&$top=1000 however this is been in beta for a number of years and very few changes seem to get made .

If you really need to get all folders and child folders you can get the graph to return the first two levels using https://graph.microsoft.com/v1.0/me/mailfolders?$top=1000&$expand=childFolders you can page in max lots of 1000 folders. With the remaining subfolders eg 3 deep check the childFolderCount and then use batching https://learn.microsoft.com/en-us/graph/json-batching with a max concurrency of 4 requests (else you'll get throttled) but similarly you can get two levels of folder using expand. The performance of this is generally not that bad as you can reduce the number of requests you need to make to a get the full hierarchy to minimum on most mailboxes the downside is it increases complexity a lot.

Answer 3

Using the GraphSDK something like

 private static void BatchChildFolders(List<string> folderIds, GraphServiceClient graphServiceClient, List<MailFolder> folders)  
         {  
             var baseRequestURL = "https://graph.microsoft.com/v1.0/Me/MailFolders";  
             BatchRequestContent batchRequestContent = new BatchRequestContent();  
             foreach (string folderid in folderIds)  
             {  
                 var childFolderBatchRequest = graphServiceClient.Teamwork.Request().GetHttpRequestMessage();  
                 string requestUrl = baseRequestURL + $"/{folderid}/childFolders?$expand=childFolders&$top=1000";  
                 childFolderBatchRequest.RequestUri = new Uri(requestUrl);  
                 batchRequestContent.AddBatchRequestStep(new BatchRequestStep(folderid, childFolderBatchRequest));  
             }  
             var batchResults = graphServiceClient.Batch.Request().PostAsync(batchRequestContent).GetAwaiter().GetResult();  
             foreach (string folderid in folderIds)  
             {  
                 using (var batchResult = batchResults.GetResponseByIdAsync(folderid).GetAwaiter().GetResult())  
                 {  
                     if (batchResult != null)  
                     {  
                         if (batchResult.StatusCode == System.Net.HttpStatusCode.OK)  
                         {                              
                             var mailFoldersResponse = batchResults.GetResponseByIdAsync<MailFolderChildFoldersCollectionResponse>(folderid).GetAwaiter().GetResult();  
                             foreach(var mailFolder in mailFoldersResponse.Value)  
                             {  
                                 Console.WriteLine(mailFolder.DisplayName);  
                             }                                 
                         }  
                         else  
                         {  
                             //errir  
                         }  
                     }  
                 }  
             }  
         }  

Where you passing in a list of FolderIds you want to batch