--Solved--
Outlook._NameSpace olNs;
Outlook.MAPIFolder oSents;
Outlook.Items oItems;
olNs = olApp.GetNamespace("MAPI");
oSents = olNs.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderSentMail);
oItems = oSents.Items;
DateTime fromDate= Convert.ToDateTime("11/21/2013");
DateTime toDate= Convert.ToDateTime("11/28/2013")
oItems = oSents.Items.Restrict("[ReceivedTime]>'" + fromDate + "' AND [ReceivedTime]<'" + toDate+ "'");