Email appending services provider FreshAddress says it's possible to find email addresses for 5-12 percent of customer names on various offline mailing lists, writes MediaPost. For its study, FreshAddress examined 100 million customer records. For commercial email senders, email addresses were found for 12 percent of individuals and 16 percent of households; there was an 8 percent success rate in the case of customers who had changed email accounts.

Email appending tends to raise eyebrows, because consumers have not directly volunteered to be contacted via an email address that they did not provide - though they may have provided an offline address or another email address.

MediaPost cites the example of one disgruntled Miller Brewing customer who had provided a "throwaway" email address for a contest but whose actual email address was ferreted out: "Not sure I like the idea of companies tracking me down like this," the consumer is quoted as having written in a blog.