Eric,
Eventhough throttling is available, won't the script still have to run in the background for a long period of time in order to send off 2,000-20,000 emails, and eventually timeout based on most webhost's php.ini settings.
I may be wrong, but please advise as I am trying to setup something similar (send enewsletter to 7,000 subscribers). Thanks.
Using DWCS5 / UE 4