i import my old users from other wordpress (just mails) blog and import them to my other blog. And tried to send them email from this plugin. But i think they didn't received it. i test it. i put my email to the list to. when i send them all (1000 mail) i didn't received it. when i put the list like 10-15 mails and mine, then i received it.
i think there is problem when mails to sending big lists.