This is a complicated question and there is no answer that fits every situation. Email companies have cracked down on spam and nefarious email campaigns. Google, especially, has implemented advanced algorithms to check for potential spam emails. Connections implements every measure to assure your emails will get to their target audience. It all begins by allowing the merchant to control the email marketing list. This is done completely through Shopify by setting the option for each customer to accept marketing. Sending emails to customers that do not opt-in for email marketing is the best way to get added to a spam list. Merchants are encouraged to ask their customers to add the email address to their contacts or safe sender list. This is the only way to gaurantee delivery.