If a new customer (buying product through your site) is added via API with setting of "ACTION_BY_CUSTOMER"s contact sent an opt-in or are they considered "double optp-in" contacts? Also, if new customer is API'ed to a specific list, does all the opt-out functionality included in any emails work the same or are you required to develop any opt-out API interfaces/web forms? Are contacts added by API/ACTION_BY_CUSTOMER not send welcome email? Thanks.
If you choose ACTION_BY_CUSTOMER, it works exactly as if you had added the contact through the user interface by using the Add/Import contacts feature. The contact would not be considered a double opt in contact unless you had this option selected in your settings.
If a customer is added to a list via the API, the opt out functionality works the same as if they were added in any other way. All contacts in our system have the option to opt out through an email newsletter.
If the contact is added by the API through ACTION_BY_CUSTOMER, they do not receive a welcome email. If they are added with ACTION_BY_CONTACT, they will receive one.