The server responded with error 50007

foreach (var user in users)
            {
                var u = user as IGuildUser;

                if (!u.IsBot && !u.IsWebhook)
                {
                    try
                    {
                        await u.SendMessageAsync("Hi");
                    }
                    catch (Exception e)
                    {
                        var useless = e;
                    }
                }
            }
[Command("dm")]
        public async Task DmAsync()
        {
            var guild = Program._client.GetGuild(Context.Guild.Id) as IGuild;
            await Context.Guild.DownloadUsersAsync();
            await Task.Delay(500);
            var users = await guild.GetUsersAsync();

            foreach (var user in users)
            {
                var u = user as IGuildUser;

                if (!u.IsBot && !u.IsWebhook)
                {
                    IUserMessage dm = await u.SendMessageAsync("Mass dm test", false);

                    if (dm == null)
                    {
                        continue;
                    }
                }
            }
        }