Tame the E-mail Tangle
Frequency. Has the customer used the same e-mail address in more than one communication with your company? If so, then this is a solid indicator of the most reliable address for him or her. Additionally, if you have the ability to track and link received e-mail communications from your customers to your marketing efforts, it will provide a powerful method for matching up a valid address to the customer.
Monetary: If you're a retailer, the more expensive a purchase, the more likely it is that the customer has provided an accurate e-mail address to ensure good communication regarding the status of his or her order. For a financial services institution that may collect e-mail information from a variety of sources, the best e-mail address may be the one linked with the most valuable account held in the customer's portfolio.
Another important consideration is the desired target audience for your message. An effective household profile would show which e-mail address to use to reach either my wife or me specifically, or which (and it would be different) should be used to reach us as a business-conducting entity. Excessive "householding" of the various e-mail addresses would reach the wrong conclusion, and send e-mail opportunities where they have little chance of meeting with success. Similar to a customer with multiple types of accounts, the customer with multiple e-mail addresses requires each address to be treated separately, and communications managed accordingly.
If you are marketing to customers with a particular account type, for example, you might choose to give more weight initially to the e-mail address associated with that specific account (perhaps in violation of the RFM rules described above).
Customers Have the Final Say
Finally, with recent legislation, care must be taken to manage e-mail-marketing preferences in accordance with customers' wishes. A customer may opt-in for a particular newsletter or specify conditions for why and how he or she should be contacted. A different e-mail address for that customer does not automatically fall under the same rule umbrella.