EmailBuddy can be integrated with iThemes Exchange.
When a customer makes a purchase on your ecommerce site, you can include a checkbox for them to sign up for your emails.
Integrating Exchange with EmailBuddy is very simple. If you haven't done so already, you'll want to go into EmailBuddy > Groups and create a group.
Once you have a group, you'll go into EmailBuddy Settings and find the iThemes Exchange Settings section (at the bottom of the settings area, just before the EmailBuddy Style Manager).
Check the box to the right of the Enable Exchange Subscription To Lists option.
This enables EmailBuddy to collect email addresses when users register on your site and gives you some options. The first option is whether or not the checkbox for the customer to sign up for your email is checked by default or not. Next, you can select which list (or group) the customer will be added to. Lastly, you can determine what the label for your checkbox will read.