DemocracyInAction's mass-mailing needs have made it a case study for scaling delivery for our own e-mail vendor, Message Systems.  It's a bit inside baseball, but if you've ever wondered about the scope of DIA's e-mailing and what's involved in making that happen quickly after you hit the "send" button ...

[A]s opposed to 100,000 messages per hour [years ago], DIA can now send 1.5 million to 2 million e-mails an hour. ...

Delivery Manager software['s] real-time analytics allows DIA to immediately identify why a message doesn't reach its intended target.

DIA's deliverability rate now nears 99 percent, and blacklisting from ISPs is no longer an issue.