Call DeleteFolder to delete folder in the opened mailbox.
function DeleteFolder(Handle: TMailboxHandle; FolderID: dword): dword;
DWORD WINAPI DeleteFolder(DWORD Handle, DWORD FolderId);
C # syntax:
static extern int DeleteFolder (int mailboxHandle, int folderId);
Identifies the mailbox file.
Id of folder to delete.
Returns OMS_OK if folder deleted, else return Error Code