Методы MoveTo, которые принимают UID (или список UID), возвращают UID (и) сообщений в папке назначения.
var uidMap = folder.MoveTo (uids, destination);
foreach (var uid in uids) {
Console.WriteLine ("The message with a UID of {0} in {1} is now {2} in {3}",
uid, folder.FullName, uidMap[uid], destination.FullName);
}