DateTime.Now.Ticks极端情况下出现了重复，换guid试试

MailSend.Web/Controllers/MailController.cs

@@ -127,7 +127,7 @@ namespace MailSend.Web.Controllers
                         {
                             var bsArr = Convert.FromBase64String(att.AttachContent);
                             var ext = Path.GetExtension(att.AttachName);
-                            var fileTmpName = DateTime.Now.Ticks.ToString();
+                            var fileTmpName = Guid.NewGuid().ToString();
                             var tempPath = Server.MapPath("~/Temp");
                             if (!Directory.Exists(tempPath))
                             {