Hi,
I 'fixed' the problem in the veterinarian sense by removing throttle limits for that domain for the moment. But the original question was in how to interpret the throttle delay choice in SM. The client's mail client was reporting 421 responses. I don't see them in the SMTP log file (at the detail level).
So does the 'throttle delay' option accept the emails and queue them, or reject the email from the client? I would assume since there is also a 'reject' option, it should do the former.
--Ben