Yea, the Opt-In Email module uses traditional SMTP...but if time is on your side:

• Now schedule newsletters to be distributed on a particular date / time -many options for scheduling newsletters including the ability to specify an amount of emails to be distributed per scheduled distribution. For example, send only 100 emails per hour until the distribution finishes. Specify the scheduler to run every based on any time frame (By minute, my hour, by day, etc...)

...perhaps you could send them out in small(er) bursts and stay under the newsletter radar. ;)

Being new to this whole DNN thing, I know of no other alternatives, but I am quite happy with all of Data Springs products...perhaps you could ask Chad over in the Data Springs forums for alternatives...