You can create Triggered Emails for when your customers' credit card that is used for Recurring Billing is set to expire. The email can be triggered to fire off of the Expiration Date. For example, you can set up an Email Message to be fired after 30 days before the expiration date.
This type of Triggered Email does not need to be assigned to a Product or Category -- it is a global Triggered Email. You can have multiple Triggered Emails of this type in your System.
Creating the Email Message
Login to the Administrative side of your database, and navigate to Settings --> Assignments --> Email Messages. Click to Add New Email. Input a Title, choose the type Triggered Recurring Billing Credit Card Expiration, and click the "Save" button.
You can now begin to compose your Email Message. Input a Subject, and add text to the Body. You can use plain text, and you can use Operators. Operators read data from the system that is relevant to the Account or Credit Card and then input that data into the email. After you are finished composing your email message, click the "Save" button.
Creating the Triggered Email
Navigate to Settings --> Assignments --> Triggered Emails. Click the "Add New Triggered Email" button. 
Input a Title, choose the Type, select your Message, choose the date range that the Triggered Email will be used, and choose what will trigger the sending of the Email Message. If you want the Triggered Email to not expire, you can select No End Date.
Choose when trigger will fire. Please note that while credit cards expire at the last of the month, the Expiration Date field in Configio is the first of the month. So, if you want to send the notification a month prior to it expiring, send it zero days before the expiration date.