By default, when a new subscription is submitted through the Recurly.js buildSubscriptionForm, the e-mail address will be used as the account_code for the newly created account. Many merchants would prefer to use their own account_code, perhaps matching their own internal code for that customer. That way when using the API or processing push notifications, there is an easy way to reference the account_code with their own internal code.
You can easily override the default option by placing the account code in your signature. Here is an example in PHP:
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