Exchange Web Service FolderId for a not well known folder name

A bit late, but the following is what I used to find my folder:

var view = new FolderView(1);
view.Traversal = FolderTraversal.Deep;
var filter = new SearchFilter.IsEqualTo(FolderSchema.DisplayName, "Rejected");
var results = Service.FindFolders(WellKnownFolderName.Root, filter, view);
if (results.TotalCount < 1)
    throw new Exception("Cannot find Rejected folder");
if (results.TotalCount > 1)
    throw new Exception("Multiple Rejected folders");
Rejected = Folder.Bind(Service, results.Folders.Single().Id);

Edit: Apparently my code did not work on nested heirarchies. I added a line as per cookiemonster's suggested edit.

The answer of seven-ply is valid, but may lead to undesired results.

Suppose you have this structure:

Root
--Folder A
----Test
--Folder B
----Test

The code he provided would return both test folders.

If you know the path (like Folder B/Test), you can get the folder path iteratively.

See my the method SetFolderHomePage in this link: http://www.infinitec.de/post/2011/10/05/Setting-the-Homepage-of-an-Exchange-folder-using-the-EWS-Managed-API.aspx.

You can find all Folders with the FindFolders method. Use WellKnownFolderName.Root to show all your folders of your Inbox. You have to create a FolderView and add the properties you want to see (ID and DisplayName for example). Set the traversal to Deep to find all of your folders. In my example, I'm looking for the folder with the DisplayName "Test".

// set Server
ExchangeService server = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
server.UseDefaultCredentials = true;
string configUrl = @"https://yourServerAddress.asmx";
server.Url = new Uri(configUrl);

// set View
FolderView view = new FolderView(100);
view.PropertySet = new PropertySet(BasePropertySet.IdOnly);
view.PropertySet.Add(FolderSchema.DisplayName);
view.Traversal = FolderTraversal.Deep;

FindFoldersResults findFolderResults = server.FindFolders(WellKnownFolderName.Root, view);

// find specific folder
foreach (Folder f in findFolderResults)
{
    // show FolderId of the folder "Test"
    if (f.DisplayName == "Test")
    {
        Console.WriteLine(f.Id);
    }
}