public EwsFolder DownloadFolderByFullName(
	FolderId containingFolderId,
	string folderFullName
)

Public Function DownloadFolderByFullName ( 
	containingFolderId As FolderId,
	folderFullName As String
) As EwsFolder

Parameters

containingFolderId

Type: FolderId
The ID of the containing folder where to search for the given folder. If a null reference (Nothing in Visual Basic), RootFolderType will be assumed.

folderFullName

Type: SystemString
The full folder name, such as "Inbox/Nested folder/Deeply nested folder". Null reference (Nothing in Visual Basic) or empty string not allowed.

Return Value

To delimit levels of hierarchy in the folder name, use the same character which is set by FolderLevelDelimiter property. By default, it's '/' (forward slash).

containingFolderId is just for optimization so you can leave it a null reference. However, if you already know that the folder you're looking for is contained in some upper level folder, you can specify it there. This will optimize performance as only a subset of all folders in the account will be searched. If you don't know the containing folder, you can use another optimization provided by DownloadFolderByFullName(string, int) overload.

containingFolderId does not need to be the immediate parent of the folder you're looking for, it can be any level up (e.g. you can specify WellKnownFolderName.Inbox while searching for "Inbox/Nested folder/Deeply nested folder"). Still, more close containingFolderId's level is to folderFullName's level - faster the search will be.

Note
This method is not implemented in .NET Core. Use DownloadFolderByFullNameAsync(FolderId, String) instead.

Reference