When customers subscribe to your service plans, they provide e-mail address as a part of their personal information. If a fragment of a subscriber's e-mail is in the Business Manager e-mail black list, and if an online store is configured to reject subscriptions from e-mails in black list, the system will not let such customers subscribe.
You can find and edit your black list at the Business Setup > All Settings > E-mail Black List page. To enable the rejection of subscriptions from e-mails in the black list for an online store, go to the Security tab of store settings page.
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