Just use
<!--email_off--> html code of dropdownlist here <!--/email_off-->
for more see below example:
<!--email_off--> @Html.DropDownListFor(m => Model.UserId, (Model.GetUsers == null ? Enumerable.Empty<selectlistitem>() : Model.GetUsers.Select(a => new SelectListItem { Text = a.Name, Value = a.ID.ToString() })), new { @class = "form-control" }) <!--/email_off-->
It's working fine.
Thanks