Yeah, I noticed this too, and posted a thread on the module forum:
http://www.magentocommerce.com/boards/viewthread/6919/

“Space” replied with a couple tips on how to possibly disable it form sending emails, but nobody has confirmed that his hack is successful at stopping the emails yet.

I tried his suggestions and ran an import but was still noticing a lot of postfix SMTP processes spinning up when I started an import, so I’m not sure if it actually fixed it or not. What I decided to do was to copy everything to my local system, disconnect the network, run the import, then make sure all postfix processes are dead and nothing is left in the queue, then rejoin the network and migrate my customer list to the live database. I really don’t want to be sending out 10,000 or so seemingly SPAM emails to customers that I want to keep happy.

It sends each email as it goes through the list of customers it’s importing, so it’s not a cron job or anything, it’s as each record is imported, it creates the customer object and stores it in the database… and somehow the creating of the customer object triggers the newseltter email.

mjohnson,

Thanks for the comment. We ended up adding a few characters in the emails on import by doing . So we added 123 before the @ sign and abc after the @ sign. In this way ensuring that no emails actually get sent to our real customers. I’m not sure if this was the best method as it probably tried sending out emails to all these domains and they all bounced. Once the import was complete we simply remove 123 and abc before and after the @ symbol.