string userIdentity = "username@domain.com";
FolderId fId = new FolderId(WellKnownFolderName.Inbox, userIdentity);
var inbox = Folder.Bind(_ews, fId);
var query = "[Test!!!]";
SearchFilter sf = new SearchFilter.ContainsSubstring(ItemSchema.Body, query, ContainmentMode.Substring, ComparisonMode.IgnoreCase);
FindItemsResults<Item> items = inbox.FindItems(sf, new ItemView(100));