HI Stefano, first of all thanks for this wonderful plugin!
i’m writing cause i’m having some problems when the user receives a newsletter email or the subscription confermation email.
Following your steps, i edited the email-alternate.php and copied to /wp-content/extensions/newsletter/subscription. If i take a look at it by browser i’m able to perfectly see all the images i embeded, but when the user receives the email he cannot see the images.
How could i solve it?