First log in to your OpenCart administrator area and navigate to Sales » Mail
"To:" field is where you can choose which of your customers the email will be sent to.
"All Newsletter Subscribers" means that the email will be sent to all the people that selected that they want to receive your regular newsletter upon their signup. This option is usefull if you want to send regular newsletters containing promotions and new product information.
"All Customers" will send the email to every customer that registered in your OpenCart store.
You can also create a custom list of users you want to email by searching for their name or email in the search box below.
The search will display the users matching this criteria in the box below the search field.
Once found select the customers you want to add to the mailing list and click on the "--->" button to move them to the right box.
You can also choose to mail all the customers who ordered a certain product from your store.
Just select the product you want and click on the "-->" button to add it to the right box.
This will make the email to be sent to all the clients that ordered the products in the right box.
Enter a subject in the "Subject Field".
And create your message using the easy editor in the "Message" box below.
Once you are ready selecting your recepients and creating the message simply click "Send" in the upper right corner of the page.
Now the emails will be sent to your customers notifying them for new products and promotions on your OpenCart online store.
Keeping your customers up to date with new products on your store is vital for your online business and keeps the sales rising.